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Nicholas Piggin

2020-Jul-02 07:48 UTC

[PATCH 0/8] powerpc: queued spinlocks and rwlocks

This series adds an option to use queued spinlocks for powerpc, and
makes it the default for the Book3S-64 subarch.

This effort starts with the generic code so it's very simple but
still very performant. There are optimisations that can be made to
slowpaths, but I think it's better to attack those incrementally
if/when we find things, and try to add the improvements to generic
code as much as possible.

Still in the process of getting numbers and testing, but the
implementation turned out to be surprisingly simple and we have a
config option, so I think we could merge it fairly soon.

Thanks,
Nick

Nicholas Piggin (8):
  powerpc/powernv: must include hvcall.h to get PAPR defines
  powerpc/pseries: use smp_rmb() in H_CONFER spin yield
  powerpc/pseries: move some PAPR paravirt functions to their own file
  powerpc: move spinlock implementation to simple_spinlock
  powerpc/64s: implement queued spinlocks and rwlocks
  powerpc/pseries: implement paravirt qspinlocks for SPLPAR
  powerpc/qspinlock: optimised atomic_try_cmpxchg_lock that adds the
    lock hint
  powerpc/64s: remove paravirt from simple spinlocks (RFC only)

 arch/powerpc/Kconfig                          |  13 +
 arch/powerpc/include/asm/Kbuild               |   2 +
 arch/powerpc/include/asm/atomic.h             |  28 ++
 arch/powerpc/include/asm/paravirt.h           |  84 +++++
 arch/powerpc/include/asm/qspinlock.h          |  75 +++++
 arch/powerpc/include/asm/qspinlock_paravirt.h |   5 +
 arch/powerpc/include/asm/simple_spinlock.h    | 235 +++++++++++++
 .../include/asm/simple_spinlock_types.h       |  21 ++
 arch/powerpc/include/asm/spinlock.h           | 308 +-----------------
 arch/powerpc/include/asm/spinlock_types.h     |  17 +-
 arch/powerpc/kvm/book3s_hv_rm_mmu.c           |   6 -
 arch/powerpc/lib/Makefile                     |   1 -
 arch/powerpc/lib/locks.c                      |  65 ----
 arch/powerpc/platforms/powernv/pci-ioda-tce.c |   1 +
 arch/powerpc/platforms/pseries/Kconfig        |   5 +
 arch/powerpc/platforms/pseries/setup.c        |   6 +-
 include/asm-generic/qspinlock.h               |   4 +
 17 files changed, 488 insertions(+), 388 deletions(-)
 create mode 100644 arch/powerpc/include/asm/paravirt.h
 create mode 100644 arch/powerpc/include/asm/qspinlock.h
 create mode 100644 arch/powerpc/include/asm/qspinlock_paravirt.h
 create mode 100644 arch/powerpc/include/asm/simple_spinlock.h
 create mode 100644 arch/powerpc/include/asm/simple_spinlock_types.h
 delete mode 100644 arch/powerpc/lib/locks.c

-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 1/8] powerpc/powernv: must include hvcall.h to get PAPR defines

An include goes away in future patches which breaks compilation
without this.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/platforms/powernv/pci-ioda-tce.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/platforms/powernv/pci-ioda-tce.c
b/arch/powerpc/platforms/powernv/pci-ioda-tce.c
index f923359d8afc..8eba6ece7808 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda-tce.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda-tce.c
@@ -15,6 +15,7 @@
 
 #include <asm/iommu.h>
 #include <asm/tce.h>
+#include <asm/hvcall.h> /* share error returns with PAPR */
 #include "pci.h"
 
 unsigned long pnv_ioda_parse_tce_sizes(struct pnv_phb *phb)
-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 2/8] powerpc/pseries: use smp_rmb() in H_CONFER spin yield

There is no need for rmb(), this allows faster lwsync here.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/lib/locks.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
index 6440d5943c00..47a530de733e 100644
--- a/arch/powerpc/lib/locks.c
+++ b/arch/powerpc/lib/locks.c
@@ -30,7 +30,7 @@ void splpar_spin_yield(arch_spinlock_t *lock)
 	yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
 	if ((yield_count & 1) == 0)
 		return;		/* virtual cpu is currently running */
-	rmb();
+	smp_rmb();
 	if (lock->slock != lock_value)
 		return;		/* something has changed */
 	plpar_hcall_norets(H_CONFER,
@@ -56,7 +56,7 @@ void splpar_rw_yield(arch_rwlock_t *rw)
 	yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
 	if ((yield_count & 1) == 0)
 		return;		/* virtual cpu is currently running */
-	rmb();
+	smp_rmb();
 	if (rw->lock != lock_value)
 		return;		/* something has changed */
 	plpar_hcall_norets(H_CONFER,
-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 3/8] powerpc/pseries: move some PAPR paravirt functions to their own file

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/paravirt.h | 61 +++++++++++++++++++++++++++++
 arch/powerpc/include/asm/spinlock.h | 24 +-----------
 arch/powerpc/lib/locks.c            | 12 +++---
 3 files changed, 68 insertions(+), 29 deletions(-)
 create mode 100644 arch/powerpc/include/asm/paravirt.h

diff --git a/arch/powerpc/include/asm/paravirt.h
b/arch/powerpc/include/asm/paravirt.h
new file mode 100644
index 000000000000..7a8546660a63
--- /dev/null
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __ASM_PARAVIRT_H
+#define __ASM_PARAVIRT_H
+#ifdef __KERNEL__
+
+#include <linux/jump_label.h>
+#include <asm/smp.h>
+#ifdef CONFIG_PPC64
+#include <asm/paca.h>
+#include <asm/hvcall.h>
+#endif
+
+#ifdef CONFIG_PPC_SPLPAR
+DECLARE_STATIC_KEY_FALSE(shared_processor);
+
+static inline bool is_shared_processor(void)
+{
+	return static_branch_unlikely(&shared_processor);
+}
+
+/* If bit 0 is set, the cpu has been preempted */
+static inline u32 yield_count_of(int cpu)
+{
+	__be32 yield_count = READ_ONCE(lppaca_of(cpu).yield_count);
+	return be32_to_cpu(yield_count);
+}
+
+static inline void yield_to_preempted(int cpu, u32 yield_count)
+{
+	plpar_hcall_norets(H_CONFER, get_hard_smp_processor_id(cpu), yield_count);
+}
+#else
+static inline bool is_shared_processor(void)
+{
+	return false;
+}
+
+static inline u32 yield_count_of(int cpu)
+{
+	return 0;
+}
+
+extern void ___bad_yield_to_preempted(void);
+static inline void yield_to_preempted(int cpu, u32 yield_count)
+{
+	___bad_yield_to_preempted(); /* This would be a bug */
+}
+#endif
+
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+	if (!is_shared_processor())
+		return false;
+	if (yield_count_of(cpu) & 1)
+		return true;
+	return false;
+}
+
+#endif /* __KERNEL__ */
+#endif /* __ASM_PARAVIRT_H */
diff --git a/arch/powerpc/include/asm/spinlock.h
b/arch/powerpc/include/asm/spinlock.h
index 2d620896cdae..79be9bb10bbb 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -15,11 +15,10 @@
  *
  * (the type definitions are in asm/spinlock_types.h)
  */
-#include <linux/jump_label.h>
 #include <linux/irqflags.h>
+#include <asm/paravirt.h>
 #ifdef CONFIG_PPC64
 #include <asm/paca.h>
-#include <asm/hvcall.h>
 #endif
 #include <asm/synch.h>
 #include <asm/ppc-opcode.h>
@@ -35,18 +34,6 @@
 #define LOCK_TOKEN	1
 #endif
 
-#ifdef CONFIG_PPC_PSERIES
-DECLARE_STATIC_KEY_FALSE(shared_processor);
-
-#define vcpu_is_preempted vcpu_is_preempted
-static inline bool vcpu_is_preempted(int cpu)
-{
-	if (!static_branch_unlikely(&shared_processor))
-		return false;
-	return !!(be32_to_cpu(lppaca_of(cpu).yield_count) & 1);
-}
-#endif
-
 static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
 {
 	return lock.slock == 0;
@@ -110,15 +97,6 @@ static inline void splpar_spin_yield(arch_spinlock_t *lock)
{};
 static inline void splpar_rw_yield(arch_rwlock_t *lock) {};
 #endif
 
-static inline bool is_shared_processor(void)
-{
-#ifdef CONFIG_PPC_SPLPAR
-	return static_branch_unlikely(&shared_processor);
-#else
-	return false;
-#endif
-}
-
 static inline void spin_yield(arch_spinlock_t *lock)
 {
 	if (is_shared_processor())
diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
index 47a530de733e..e35fd1a16992 100644
--- a/arch/powerpc/lib/locks.c
+++ b/arch/powerpc/lib/locks.c
@@ -27,14 +27,14 @@ void splpar_spin_yield(arch_spinlock_t *lock)
 		return;
 	holder_cpu = lock_value & 0xffff;
 	BUG_ON(holder_cpu >= NR_CPUS);
-	yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
+
+	yield_count = yield_count_of(holder_cpu);
 	if ((yield_count & 1) == 0)
 		return;		/* virtual cpu is currently running */
 	smp_rmb();
 	if (lock->slock != lock_value)
 		return;		/* something has changed */
-	plpar_hcall_norets(H_CONFER,
-		get_hard_smp_processor_id(holder_cpu), yield_count);
+	yield_to_preempted(holder_cpu, yield_count);
 }
 EXPORT_SYMBOL_GPL(splpar_spin_yield);
 
@@ -53,13 +53,13 @@ void splpar_rw_yield(arch_rwlock_t *rw)
 		return;		/* no write lock at present */
 	holder_cpu = lock_value & 0xffff;
 	BUG_ON(holder_cpu >= NR_CPUS);
-	yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
+
+	yield_count = yield_count_of(holder_cpu);
 	if ((yield_count & 1) == 0)
 		return;		/* virtual cpu is currently running */
 	smp_rmb();
 	if (rw->lock != lock_value)
 		return;		/* something has changed */
-	plpar_hcall_norets(H_CONFER,
-		get_hard_smp_processor_id(holder_cpu), yield_count);
+	yield_to_preempted(holder_cpu, yield_count);
 }
 #endif
-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 4/8] powerpc: move spinlock implementation to simple_spinlock

To prepare for queued spinlocks. This is a simple rename except to update
preprocessor guard name and a file reference.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/simple_spinlock.h    | 292 ++++++++++++++++++
 .../include/asm/simple_spinlock_types.h       |  21 ++
 arch/powerpc/include/asm/spinlock.h           | 285 +----------------
 arch/powerpc/include/asm/spinlock_types.h     |  12 +-
 4 files changed, 315 insertions(+), 295 deletions(-)
 create mode 100644 arch/powerpc/include/asm/simple_spinlock.h
 create mode 100644 arch/powerpc/include/asm/simple_spinlock_types.h

diff --git a/arch/powerpc/include/asm/simple_spinlock.h
b/arch/powerpc/include/asm/simple_spinlock.h
new file mode 100644
index 000000000000..e048c041c4a9
--- /dev/null
+++ b/arch/powerpc/include/asm/simple_spinlock.h
@@ -0,0 +1,292 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __ASM_SIMPLE_SPINLOCK_H
+#define __ASM_SIMPLE_SPINLOCK_H
+#ifdef __KERNEL__
+
+/*
+ * Simple spin lock operations.  
+ *
+ * Copyright (C) 2001-2004 Paul Mackerras <paulus at au.ibm.com>, IBM
+ * Copyright (C) 2001 Anton Blanchard <anton at au.ibm.com>, IBM
+ * Copyright (C) 2002 Dave Engebretsen <engebret at us.ibm.com>, IBM
+ *	Rework to support virtual processors
+ *
+ * Type of int is used as a full 64b word is not necessary.
+ *
+ * (the type definitions are in asm/simple_spinlock_types.h)
+ */
+#include <linux/irqflags.h>
+#include <asm/paravirt.h>
+#ifdef CONFIG_PPC64
+#include <asm/paca.h>
+#endif
+#include <asm/synch.h>
+#include <asm/ppc-opcode.h>
+
+#ifdef CONFIG_PPC64
+/* use 0x800000yy when locked, where yy == CPU number */
+#ifdef __BIG_ENDIAN__
+#define LOCK_TOKEN	(*(u32 *)(&get_paca()->lock_token))
+#else
+#define LOCK_TOKEN	(*(u32 *)(&get_paca()->paca_index))
+#endif
+#else
+#define LOCK_TOKEN	1
+#endif
+
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+	return lock.slock == 0;
+}
+
+static inline int arch_spin_is_locked(arch_spinlock_t *lock)
+{
+	smp_mb();
+	return !arch_spin_value_unlocked(*lock);
+}
+
+/*
+ * This returns the old value in the lock, so we succeeded
+ * in getting the lock if the return value is 0.
+ */
+static inline unsigned long __arch_spin_trylock(arch_spinlock_t *lock)
+{
+	unsigned long tmp, token;
+
+	token = LOCK_TOKEN;
+	__asm__ __volatile__(
+"1:	" PPC_LWARX(%0,0,%2,1) "\n\
+	cmpwi		0,%0,0\n\
+	bne-		2f\n\
+	stwcx.		%1,0,%2\n\
+	bne-		1b\n"
+	PPC_ACQUIRE_BARRIER
+"2:"
+	: "=&r" (tmp)
+	: "r" (token), "r" (&lock->slock)
+	: "cr0", "memory");
+
+	return tmp;
+}
+
+static inline int arch_spin_trylock(arch_spinlock_t *lock)
+{
+	return __arch_spin_trylock(lock) == 0;
+}
+
+/*
+ * On a system with shared processors (that is, where a physical
+ * processor is multiplexed between several virtual processors),
+ * there is no point spinning on a lock if the holder of the lock
+ * isn't currently scheduled on a physical processor.  Instead
+ * we detect this situation and ask the hypervisor to give the
+ * rest of our timeslice to the lock holder.
+ *
+ * So that we can tell which virtual processor is holding a lock,
+ * we put 0x80000000 | smp_processor_id() in the lock when it is
+ * held.  Conveniently, we have a word in the paca that holds this
+ * value.
+ */
+
+#if defined(CONFIG_PPC_SPLPAR)
+/* We only yield to the hypervisor if we are in shared processor mode */
+void splpar_spin_yield(arch_spinlock_t *lock);
+void splpar_rw_yield(arch_rwlock_t *lock);
+#else /* SPLPAR */
+static inline void splpar_spin_yield(arch_spinlock_t *lock) {};
+static inline void splpar_rw_yield(arch_rwlock_t *lock) {};
+#endif
+
+static inline void spin_yield(arch_spinlock_t *lock)
+{
+	if (is_shared_processor())
+		splpar_spin_yield(lock);
+	else
+		barrier();
+}
+
+static inline void rw_yield(arch_rwlock_t *lock)
+{
+	if (is_shared_processor())
+		splpar_rw_yield(lock);
+	else
+		barrier();
+}
+
+static inline void arch_spin_lock(arch_spinlock_t *lock)
+{
+	while (1) {
+		if (likely(__arch_spin_trylock(lock) == 0))
+			break;
+		do {
+			HMT_low();
+			if (is_shared_processor())
+				splpar_spin_yield(lock);
+		} while (unlikely(lock->slock != 0));
+		HMT_medium();
+	}
+}
+
+static inline
+void arch_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
+{
+	unsigned long flags_dis;
+
+	while (1) {
+		if (likely(__arch_spin_trylock(lock) == 0))
+			break;
+		local_save_flags(flags_dis);
+		local_irq_restore(flags);
+		do {
+			HMT_low();
+			if (is_shared_processor())
+				splpar_spin_yield(lock);
+		} while (unlikely(lock->slock != 0));
+		HMT_medium();
+		local_irq_restore(flags_dis);
+	}
+}
+#define arch_spin_lock_flags arch_spin_lock_flags
+
+static inline void arch_spin_unlock(arch_spinlock_t *lock)
+{
+	__asm__ __volatile__("# arch_spin_unlock\n\t"
+				PPC_RELEASE_BARRIER: : :"memory");
+	lock->slock = 0;
+}
+
+/*
+ * Read-write spinlocks, allowing multiple readers
+ * but only one writer.
+ *
+ * NOTE! it is quite common to have readers in interrupts
+ * but no interrupt writers. For those circumstances we
+ * can "mix" irq-safe locks - any writer needs to get a
+ * irq-safe write-lock, but readers can get non-irqsafe
+ * read-locks.
+ */
+
+#ifdef CONFIG_PPC64
+#define __DO_SIGN_EXTEND	"extsw	%0,%0\n"
+#define WRLOCK_TOKEN		LOCK_TOKEN	/* it's negative */
+#else
+#define __DO_SIGN_EXTEND
+#define WRLOCK_TOKEN		(-1)
+#endif
+
+/*
+ * This returns the old value in the lock + 1,
+ * so we got a read lock if the return value is > 0.
+ */
+static inline long __arch_read_trylock(arch_rwlock_t *rw)
+{
+	long tmp;
+
+	__asm__ __volatile__(
+"1:	" PPC_LWARX(%0,0,%1,1) "\n"
+	__DO_SIGN_EXTEND
+"	addic.		%0,%0,1\n\
+	ble-		2f\n"
+"	stwcx.		%0,0,%1\n\
+	bne-		1b\n"
+	PPC_ACQUIRE_BARRIER
+"2:"	: "=&r" (tmp)
+	: "r" (&rw->lock)
+	: "cr0", "xer", "memory");
+
+	return tmp;
+}
+
+/*
+ * This returns the old value in the lock,
+ * so we got the write lock if the return value is 0.
+ */
+static inline long __arch_write_trylock(arch_rwlock_t *rw)
+{
+	long tmp, token;
+
+	token = WRLOCK_TOKEN;
+	__asm__ __volatile__(
+"1:	" PPC_LWARX(%0,0,%2,1) "\n\
+	cmpwi		0,%0,0\n\
+	bne-		2f\n"
+"	stwcx.		%1,0,%2\n\
+	bne-		1b\n"
+	PPC_ACQUIRE_BARRIER
+"2:"	: "=&r" (tmp)
+	: "r" (token), "r" (&rw->lock)
+	: "cr0", "memory");
+
+	return tmp;
+}
+
+static inline void arch_read_lock(arch_rwlock_t *rw)
+{
+	while (1) {
+		if (likely(__arch_read_trylock(rw) > 0))
+			break;
+		do {
+			HMT_low();
+			if (is_shared_processor())
+				splpar_rw_yield(rw);
+		} while (unlikely(rw->lock < 0));
+		HMT_medium();
+	}
+}
+
+static inline void arch_write_lock(arch_rwlock_t *rw)
+{
+	while (1) {
+		if (likely(__arch_write_trylock(rw) == 0))
+			break;
+		do {
+			HMT_low();
+			if (is_shared_processor())
+				splpar_rw_yield(rw);
+		} while (unlikely(rw->lock != 0));
+		HMT_medium();
+	}
+}
+
+static inline int arch_read_trylock(arch_rwlock_t *rw)
+{
+	return __arch_read_trylock(rw) > 0;
+}
+
+static inline int arch_write_trylock(arch_rwlock_t *rw)
+{
+	return __arch_write_trylock(rw) == 0;
+}
+
+static inline void arch_read_unlock(arch_rwlock_t *rw)
+{
+	long tmp;
+
+	__asm__ __volatile__(
+	"# read_unlock\n\t"
+	PPC_RELEASE_BARRIER
+"1:	lwarx		%0,0,%1\n\
+	addic		%0,%0,-1\n"
+"	stwcx.		%0,0,%1\n\
+	bne-		1b"
+	: "=&r"(tmp)
+	: "r"(&rw->lock)
+	: "cr0", "xer", "memory");
+}
+
+static inline void arch_write_unlock(arch_rwlock_t *rw)
+{
+	__asm__ __volatile__("# write_unlock\n\t"
+				PPC_RELEASE_BARRIER: : :"memory");
+	rw->lock = 0;
+}
+
+#define arch_spin_relax(lock)	spin_yield(lock)
+#define arch_read_relax(lock)	rw_yield(lock)
+#define arch_write_relax(lock)	rw_yield(lock)
+
+/* See include/linux/spinlock.h */
+#define smp_mb__after_spinlock()   smp_mb()
+
+#endif /* __KERNEL__ */
+#endif /* __ASM_SIMPLE_SPINLOCK_H */
diff --git a/arch/powerpc/include/asm/simple_spinlock_types.h
b/arch/powerpc/include/asm/simple_spinlock_types.h
new file mode 100644
index 000000000000..7c2b48ce62dc
--- /dev/null
+++ b/arch/powerpc/include/asm/simple_spinlock_types.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_POWERPC_SIMPLE_SPINLOCK_TYPES_H
+#define _ASM_POWERPC_SIMPLE_SPINLOCK_TYPES_H
+
+#ifndef __LINUX_SPINLOCK_TYPES_H
+# error "please don't include this file directly"
+#endif
+
+typedef struct {
+	volatile unsigned int slock;
+} arch_spinlock_t;
+
+#define __ARCH_SPIN_LOCK_UNLOCKED	{ 0 }
+
+typedef struct {
+	volatile signed int lock;
+} arch_rwlock_t;
+
+#define __ARCH_RW_LOCK_UNLOCKED		{ 0 }
+
+#endif
diff --git a/arch/powerpc/include/asm/spinlock.h
b/arch/powerpc/include/asm/spinlock.h
index 79be9bb10bbb..21357fe05fe0 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -3,290 +3,7 @@
 #define __ASM_SPINLOCK_H
 #ifdef __KERNEL__
 
-/*
- * Simple spin lock operations.  
- *
- * Copyright (C) 2001-2004 Paul Mackerras <paulus at au.ibm.com>, IBM
- * Copyright (C) 2001 Anton Blanchard <anton at au.ibm.com>, IBM
- * Copyright (C) 2002 Dave Engebretsen <engebret at us.ibm.com>, IBM
- *	Rework to support virtual processors
- *
- * Type of int is used as a full 64b word is not necessary.
- *
- * (the type definitions are in asm/spinlock_types.h)
- */
-#include <linux/irqflags.h>
-#include <asm/paravirt.h>
-#ifdef CONFIG_PPC64
-#include <asm/paca.h>
-#endif
-#include <asm/synch.h>
-#include <asm/ppc-opcode.h>
-
-#ifdef CONFIG_PPC64
-/* use 0x800000yy when locked, where yy == CPU number */
-#ifdef __BIG_ENDIAN__
-#define LOCK_TOKEN	(*(u32 *)(&get_paca()->lock_token))
-#else
-#define LOCK_TOKEN	(*(u32 *)(&get_paca()->paca_index))
-#endif
-#else
-#define LOCK_TOKEN	1
-#endif
-
-static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-{
-	return lock.slock == 0;
-}
-
-static inline int arch_spin_is_locked(arch_spinlock_t *lock)
-{
-	smp_mb();
-	return !arch_spin_value_unlocked(*lock);
-}
-
-/*
- * This returns the old value in the lock, so we succeeded
- * in getting the lock if the return value is 0.
- */
-static inline unsigned long __arch_spin_trylock(arch_spinlock_t *lock)
-{
-	unsigned long tmp, token;
-
-	token = LOCK_TOKEN;
-	__asm__ __volatile__(
-"1:	" PPC_LWARX(%0,0,%2,1) "\n\
-	cmpwi		0,%0,0\n\
-	bne-		2f\n\
-	stwcx.		%1,0,%2\n\
-	bne-		1b\n"
-	PPC_ACQUIRE_BARRIER
-"2:"
-	: "=&r" (tmp)
-	: "r" (token), "r" (&lock->slock)
-	: "cr0", "memory");
-
-	return tmp;
-}
-
-static inline int arch_spin_trylock(arch_spinlock_t *lock)
-{
-	return __arch_spin_trylock(lock) == 0;
-}
-
-/*
- * On a system with shared processors (that is, where a physical
- * processor is multiplexed between several virtual processors),
- * there is no point spinning on a lock if the holder of the lock
- * isn't currently scheduled on a physical processor.  Instead
- * we detect this situation and ask the hypervisor to give the
- * rest of our timeslice to the lock holder.
- *
- * So that we can tell which virtual processor is holding a lock,
- * we put 0x80000000 | smp_processor_id() in the lock when it is
- * held.  Conveniently, we have a word in the paca that holds this
- * value.
- */
-
-#if defined(CONFIG_PPC_SPLPAR)
-/* We only yield to the hypervisor if we are in shared processor mode */
-void splpar_spin_yield(arch_spinlock_t *lock);
-void splpar_rw_yield(arch_rwlock_t *lock);
-#else /* SPLPAR */
-static inline void splpar_spin_yield(arch_spinlock_t *lock) {};
-static inline void splpar_rw_yield(arch_rwlock_t *lock) {};
-#endif
-
-static inline void spin_yield(arch_spinlock_t *lock)
-{
-	if (is_shared_processor())
-		splpar_spin_yield(lock);
-	else
-		barrier();
-}
-
-static inline void rw_yield(arch_rwlock_t *lock)
-{
-	if (is_shared_processor())
-		splpar_rw_yield(lock);
-	else
-		barrier();
-}
-
-static inline void arch_spin_lock(arch_spinlock_t *lock)
-{
-	while (1) {
-		if (likely(__arch_spin_trylock(lock) == 0))
-			break;
-		do {
-			HMT_low();
-			if (is_shared_processor())
-				splpar_spin_yield(lock);
-		} while (unlikely(lock->slock != 0));
-		HMT_medium();
-	}
-}
-
-static inline
-void arch_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
-{
-	unsigned long flags_dis;
-
-	while (1) {
-		if (likely(__arch_spin_trylock(lock) == 0))
-			break;
-		local_save_flags(flags_dis);
-		local_irq_restore(flags);
-		do {
-			HMT_low();
-			if (is_shared_processor())
-				splpar_spin_yield(lock);
-		} while (unlikely(lock->slock != 0));
-		HMT_medium();
-		local_irq_restore(flags_dis);
-	}
-}
-#define arch_spin_lock_flags arch_spin_lock_flags
-
-static inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
-	__asm__ __volatile__("# arch_spin_unlock\n\t"
-				PPC_RELEASE_BARRIER: : :"memory");
-	lock->slock = 0;
-}
-
-/*
- * Read-write spinlocks, allowing multiple readers
- * but only one writer.
- *
- * NOTE! it is quite common to have readers in interrupts
- * but no interrupt writers. For those circumstances we
- * can "mix" irq-safe locks - any writer needs to get a
- * irq-safe write-lock, but readers can get non-irqsafe
- * read-locks.
- */
-
-#ifdef CONFIG_PPC64
-#define __DO_SIGN_EXTEND	"extsw	%0,%0\n"
-#define WRLOCK_TOKEN		LOCK_TOKEN	/* it's negative */
-#else
-#define __DO_SIGN_EXTEND
-#define WRLOCK_TOKEN		(-1)
-#endif
-
-/*
- * This returns the old value in the lock + 1,
- * so we got a read lock if the return value is > 0.
- */
-static inline long __arch_read_trylock(arch_rwlock_t *rw)
-{
-	long tmp;
-
-	__asm__ __volatile__(
-"1:	" PPC_LWARX(%0,0,%1,1) "\n"
-	__DO_SIGN_EXTEND
-"	addic.		%0,%0,1\n\
-	ble-		2f\n"
-"	stwcx.		%0,0,%1\n\
-	bne-		1b\n"
-	PPC_ACQUIRE_BARRIER
-"2:"	: "=&r" (tmp)
-	: "r" (&rw->lock)
-	: "cr0", "xer", "memory");
-
-	return tmp;
-}
-
-/*
- * This returns the old value in the lock,
- * so we got the write lock if the return value is 0.
- */
-static inline long __arch_write_trylock(arch_rwlock_t *rw)
-{
-	long tmp, token;
-
-	token = WRLOCK_TOKEN;
-	__asm__ __volatile__(
-"1:	" PPC_LWARX(%0,0,%2,1) "\n\
-	cmpwi		0,%0,0\n\
-	bne-		2f\n"
-"	stwcx.		%1,0,%2\n\
-	bne-		1b\n"
-	PPC_ACQUIRE_BARRIER
-"2:"	: "=&r" (tmp)
-	: "r" (token), "r" (&rw->lock)
-	: "cr0", "memory");
-
-	return tmp;
-}
-
-static inline void arch_read_lock(arch_rwlock_t *rw)
-{
-	while (1) {
-		if (likely(__arch_read_trylock(rw) > 0))
-			break;
-		do {
-			HMT_low();
-			if (is_shared_processor())
-				splpar_rw_yield(rw);
-		} while (unlikely(rw->lock < 0));
-		HMT_medium();
-	}
-}
-
-static inline void arch_write_lock(arch_rwlock_t *rw)
-{
-	while (1) {
-		if (likely(__arch_write_trylock(rw) == 0))
-			break;
-		do {
-			HMT_low();
-			if (is_shared_processor())
-				splpar_rw_yield(rw);
-		} while (unlikely(rw->lock != 0));
-		HMT_medium();
-	}
-}
-
-static inline int arch_read_trylock(arch_rwlock_t *rw)
-{
-	return __arch_read_trylock(rw) > 0;
-}
-
-static inline int arch_write_trylock(arch_rwlock_t *rw)
-{
-	return __arch_write_trylock(rw) == 0;
-}
-
-static inline void arch_read_unlock(arch_rwlock_t *rw)
-{
-	long tmp;
-
-	__asm__ __volatile__(
-	"# read_unlock\n\t"
-	PPC_RELEASE_BARRIER
-"1:	lwarx		%0,0,%1\n\
-	addic		%0,%0,-1\n"
-"	stwcx.		%0,0,%1\n\
-	bne-		1b"
-	: "=&r"(tmp)
-	: "r"(&rw->lock)
-	: "cr0", "xer", "memory");
-}
-
-static inline void arch_write_unlock(arch_rwlock_t *rw)
-{
-	__asm__ __volatile__("# write_unlock\n\t"
-				PPC_RELEASE_BARRIER: : :"memory");
-	rw->lock = 0;
-}
-
-#define arch_spin_relax(lock)	spin_yield(lock)
-#define arch_read_relax(lock)	rw_yield(lock)
-#define arch_write_relax(lock)	rw_yield(lock)
-
-/* See include/linux/spinlock.h */
-#define smp_mb__after_spinlock()   smp_mb()
+#include <asm/simple_spinlock.h>
 
 #endif /* __KERNEL__ */
 #endif /* __ASM_SPINLOCK_H */
diff --git a/arch/powerpc/include/asm/spinlock_types.h
b/arch/powerpc/include/asm/spinlock_types.h
index 87adaf13b7e8..3906f52dae65 100644
--- a/arch/powerpc/include/asm/spinlock_types.h
+++ b/arch/powerpc/include/asm/spinlock_types.h
@@ -6,16 +6,6 @@
 # error "please don't include this file directly"
 #endif
 
-typedef struct {
-	volatile unsigned int slock;
-} arch_spinlock_t;
-
-#define __ARCH_SPIN_LOCK_UNLOCKED	{ 0 }
-
-typedef struct {
-	volatile signed int lock;
-} arch_rwlock_t;
-
-#define __ARCH_RW_LOCK_UNLOCKED		{ 0 }
+#include <asm/simple_spinlock_types.h>
 
 #endif
-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 5/8] powerpc/64s: implement queued spinlocks and rwlocks

These have shown significantly improved performance and fairness when
spinlock contention is moderate to high on very large systems.

 [ Numbers hopefully forthcoming after more testing, but initial
   results look good ]

Thanks to the fast path, single threaded performance is not noticably
hurt.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/Kconfig                      | 13 +++++++++++++
 arch/powerpc/include/asm/Kbuild           |  2 ++
 arch/powerpc/include/asm/qspinlock.h      | 20 ++++++++++++++++++++
 arch/powerpc/include/asm/spinlock.h       |  5 +++++
 arch/powerpc/include/asm/spinlock_types.h |  5 +++++
 arch/powerpc/lib/Makefile                 |  3 +++
 include/asm-generic/qspinlock.h           |  2 ++
 7 files changed, 50 insertions(+)
 create mode 100644 arch/powerpc/include/asm/qspinlock.h

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 9fa23eb320ff..b17575109876 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -145,6 +145,8 @@ config PPC
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
+	select ARCH_USE_QUEUED_RWLOCKS		if PPC_QUEUED_SPINLOCKS
+	select ARCH_USE_QUEUED_SPINLOCKS	if PPC_QUEUED_SPINLOCKS
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select ARCH_WEAK_RELEASE_ACQUIRE
 	select BINFMT_ELF
@@ -490,6 +492,17 @@ config HOTPLUG_CPU
 
 	  Say N if you are unsure.
 
+config PPC_QUEUED_SPINLOCKS
+	bool "Queued spinlocks"
+	depends on SMP
+	default "y" if PPC_BOOK3S_64
+	help
+	  Say Y here to use to use queued spinlocks which are more complex
+	  but give better salability and fairness on large SMP and NUMA
+	  systems.
+
+	  If unsure, say "Y" if you have lots of cores, otherwise
"N".
+
 config ARCH_CPU_PROBE_RELEASE
 	def_bool y
 	depends on HOTPLUG_CPU
diff --git a/arch/powerpc/include/asm/Kbuild b/arch/powerpc/include/asm/Kbuild
index dadbcf3a0b1e..1dd8b6adff5e 100644
--- a/arch/powerpc/include/asm/Kbuild
+++ b/arch/powerpc/include/asm/Kbuild
@@ -6,5 +6,7 @@ generated-y += syscall_table_spu.h
 generic-y += export.h
 generic-y += local64.h
 generic-y += mcs_spinlock.h
+generic-y += qrwlock.h
+generic-y += qspinlock.h
 generic-y += vtime.h
 generic-y += early_ioremap.h
diff --git a/arch/powerpc/include/asm/qspinlock.h
b/arch/powerpc/include/asm/qspinlock.h
new file mode 100644
index 000000000000..f84da77b6bb7
--- /dev/null
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_POWERPC_QSPINLOCK_H
+#define _ASM_POWERPC_QSPINLOCK_H
+
+#include <asm-generic/qspinlock_types.h>
+
+#define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */
+
+#define smp_mb__after_spinlock()   smp_mb()
+
+static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
+{
+	smp_mb();
+	return atomic_read(&lock->val);
+}
+#define queued_spin_is_locked queued_spin_is_locked
+
+#include <asm-generic/qspinlock.h>
+
+#endif /* _ASM_POWERPC_QSPINLOCK_H */
diff --git a/arch/powerpc/include/asm/spinlock.h
b/arch/powerpc/include/asm/spinlock.h
index 21357fe05fe0..434615f1d761 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -3,7 +3,12 @@
 #define __ASM_SPINLOCK_H
 #ifdef __KERNEL__
 
+#ifdef CONFIG_PPC_QUEUED_SPINLOCKS
+#include <asm/qspinlock.h>
+#include <asm/qrwlock.h>
+#else
 #include <asm/simple_spinlock.h>
+#endif
 
 #endif /* __KERNEL__ */
 #endif /* __ASM_SPINLOCK_H */
diff --git a/arch/powerpc/include/asm/spinlock_types.h
b/arch/powerpc/include/asm/spinlock_types.h
index 3906f52dae65..c5d742f18021 100644
--- a/arch/powerpc/include/asm/spinlock_types.h
+++ b/arch/powerpc/include/asm/spinlock_types.h
@@ -6,6 +6,11 @@
 # error "please don't include this file directly"
 #endif
 
+#ifdef CONFIG_PPC_QUEUED_SPINLOCKS
+#include <asm-generic/qspinlock_types.h>
+#include <asm-generic/qrwlock_types.h>
+#else
 #include <asm/simple_spinlock_types.h>
+#endif
 
 #endif
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 5e994cda8e40..d66a645503eb 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -41,7 +41,10 @@ obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o
copypage_power7.o \
 obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
 	   memcpy_64.o memcpy_mcsafe_64.o
 
+ifndef CONFIG_PPC_QUEUED_SPINLOCKS
 obj64-$(CONFIG_SMP)	+= locks.o
+endif
+
 obj64-$(CONFIG_ALTIVEC)	+= vmx-helper.o
 obj64-$(CONFIG_KPROBES_SANITY_TEST)	+= test_emulate_step.o \
 					   test_emulate_step_exec_instr.o
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index fde943d180e0..fb0a814d4395 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -12,6 +12,7 @@
 
 #include <asm-generic/qspinlock_types.h>
 
+#ifndef queued_spin_is_locked
 /**
  * queued_spin_is_locked - is the spinlock locked?
  * @lock: Pointer to queued spinlock structure
@@ -25,6 +26,7 @@ static __always_inline int queued_spin_is_locked(struct
qspinlock *lock)
 	 */
 	return atomic_read(&lock->val);
 }
+#endif
 
 /**
  * queued_spin_value_unlocked - is the spinlock structure unlocked?
-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 6/8] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/paravirt.h           | 23 ++++++++
 arch/powerpc/include/asm/qspinlock.h          | 55 +++++++++++++++++++
 arch/powerpc/include/asm/qspinlock_paravirt.h |  5 ++
 arch/powerpc/platforms/pseries/Kconfig        |  5 ++
 arch/powerpc/platforms/pseries/setup.c        |  6 +-
 include/asm-generic/qspinlock.h               |  2 +
 6 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 arch/powerpc/include/asm/qspinlock_paravirt.h

diff --git a/arch/powerpc/include/asm/paravirt.h
b/arch/powerpc/include/asm/paravirt.h
index 7a8546660a63..5fae9dfa6fe9 100644
--- a/arch/powerpc/include/asm/paravirt.h
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -29,6 +29,16 @@ static inline void yield_to_preempted(int cpu, u32
yield_count)
 {
 	plpar_hcall_norets(H_CONFER, get_hard_smp_processor_id(cpu), yield_count);
 }
+
+static inline void prod_cpu(int cpu)
+{
+	plpar_hcall_norets(H_PROD, get_hard_smp_processor_id(cpu));
+}
+
+static inline void yield_to_any(void)
+{
+	plpar_hcall_norets(H_CONFER, -1, 0);
+}
 #else
 static inline bool is_shared_processor(void)
 {
@@ -45,6 +55,19 @@ static inline void yield_to_preempted(int cpu, u32
yield_count)
 {
 	___bad_yield_to_preempted(); /* This would be a bug */
 }
+
+extern void ___bad_yield_to_any(void);
+static inline void yield_to_any(void)
+{
+	___bad_yield_to_any(); /* This would be a bug */
+}
+
+extern void ___bad_prod_cpu(void);
+static inline void prod_cpu(int cpu)
+{
+	___bad_prod_cpu(); /* This would be a bug */
+}
+
 #endif
 
 #define vcpu_is_preempted vcpu_is_preempted
diff --git a/arch/powerpc/include/asm/qspinlock.h
b/arch/powerpc/include/asm/qspinlock.h
index f84da77b6bb7..997a9a32df77 100644
--- a/arch/powerpc/include/asm/qspinlock.h
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -3,9 +3,36 @@
 #define _ASM_POWERPC_QSPINLOCK_H
 
 #include <asm-generic/qspinlock_types.h>
+#include <asm/paravirt.h>
 
 #define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */
 
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+
+static __always_inline void queued_spin_lock_slowpath(struct qspinlock *lock,
u32 val)
+{
+	if (!is_shared_processor())
+		native_queued_spin_lock_slowpath(lock, val);
+	else
+		__pv_queued_spin_lock_slowpath(lock, val);
+}
+#else
+extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+#endif
+
+static __always_inline void queued_spin_lock(struct qspinlock *lock)
+{
+	u32 val = 0;
+
+	if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val,
_Q_LOCKED_VAL)))
+		return;
+
+	queued_spin_lock_slowpath(lock, val);
+}
+#define queued_spin_lock queued_spin_lock
+
 #define smp_mb__after_spinlock()   smp_mb()
 
 static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
@@ -15,6 +42,34 @@ static __always_inline int queued_spin_is_locked(struct
qspinlock *lock)
 }
 #define queued_spin_is_locked queued_spin_is_locked
 
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#define SPIN_THRESHOLD (1<<15) /* not tuned */
+
+static __always_inline void pv_wait(u8 *ptr, u8 val)
+{
+	if (*ptr != val)
+		return;
+	yield_to_any();
+	/*
+	 * We could pass in a CPU here if waiting in the queue and yield to
+	 * the previous CPU in the queue.
+	 */
+}
+
+static __always_inline void pv_kick(int cpu)
+{
+	prod_cpu(cpu);
+}
+
+extern void __pv_init_lock_hash(void);
+
+static inline void pv_spinlocks_init(void)
+{
+	__pv_init_lock_hash();
+}
+
+#endif
+
 #include <asm-generic/qspinlock.h>
 
 #endif /* _ASM_POWERPC_QSPINLOCK_H */
diff --git a/arch/powerpc/include/asm/qspinlock_paravirt.h
b/arch/powerpc/include/asm/qspinlock_paravirt.h
new file mode 100644
index 000000000000..6dbdb8a4f84f
--- /dev/null
+++ b/arch/powerpc/include/asm/qspinlock_paravirt.h
@@ -0,0 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __ASM_QSPINLOCK_PARAVIRT_H
+#define __ASM_QSPINLOCK_PARAVIRT_H
+
+#endif /* __ASM_QSPINLOCK_PARAVIRT_H */
diff --git a/arch/powerpc/platforms/pseries/Kconfig
b/arch/powerpc/platforms/pseries/Kconfig
index 24c18362e5ea..756e727b383f 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -25,9 +25,14 @@ config PPC_PSERIES
 	select SWIOTLB
 	default y
 
+config PARAVIRT_SPINLOCKS
+	bool
+	default n
+
 config PPC_SPLPAR
 	depends on PPC_PSERIES
 	bool "Support for shared-processor logical partitions"
+	select PARAVIRT_SPINLOCKS if PPC_QUEUED_SPINLOCKS
 	help
 	  Enabling this option will make the kernel run more efficiently
 	  on logically-partitioned pSeries systems which use shared
diff --git a/arch/powerpc/platforms/pseries/setup.c
b/arch/powerpc/platforms/pseries/setup.c
index 2db8469e475f..747a203d9453 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -771,8 +771,12 @@ static void __init pSeries_setup_arch(void)
 	if (firmware_has_feature(FW_FEATURE_LPAR)) {
 		vpa_init(boot_cpuid);
 
-		if (lppaca_shared_proc(get_lppaca()))
+		if (lppaca_shared_proc(get_lppaca())) {
 			static_branch_enable(&shared_processor);
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+			pv_spinlocks_init();
+#endif
+		}
 
 		ppc_md.power_save = pseries_lpar_idle;
 		ppc_md.enable_pmcs = pseries_lpar_enable_pmcs;
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index fb0a814d4395..38ca14e79a86 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -69,6 +69,7 @@ static __always_inline int queued_spin_trylock(struct
qspinlock *lock)
 
 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
 
+#ifndef queued_spin_lock
 /**
  * queued_spin_lock - acquire a queued spinlock
  * @lock: Pointer to queued spinlock structure
@@ -82,6 +83,7 @@ static __always_inline void queued_spin_lock(struct qspinlock
*lock)
 
 	queued_spin_lock_slowpath(lock, val);
 }
+#endif
 
 #ifndef queued_spin_unlock
 /**
-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 7/8] powerpc/qspinlock: optimised atomic_try_cmpxchg_lock that adds the lock hint

This brings the behaviour of the uncontended fast path back to
roughly equivalent to simple spinlocks -- a single atomic op with
lock hint.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/atomic.h    | 28 ++++++++++++++++++++++++++++
 arch/powerpc/include/asm/qspinlock.h |  2 +-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/atomic.h
b/arch/powerpc/include/asm/atomic.h
index 498785ffc25f..f6a3d145ffb7 100644
--- a/arch/powerpc/include/asm/atomic.h
+++ b/arch/powerpc/include/asm/atomic.h
@@ -193,6 +193,34 @@ static __inline__ int atomic_dec_return_relaxed(atomic_t
*v)
 #define atomic_xchg(v, new) (xchg(&((v)->counter), new))
 #define atomic_xchg_relaxed(v, new) xchg_relaxed(&((v)->counter), (new))
 
+/*
+ * Don't want to override the generic atomic_try_cmpxchg_acquire, because
+ * we add a lock hint to the lwarx, which may not be wanted for the
+ * _acquire case (and is not used by the other _acquire variants so it
+ * would be a surprise).
+ */
+static __always_inline bool
+atomic_try_cmpxchg_lock(atomic_t *v, int *old, int new)
+{
+	int r, o = *old;
+
+	__asm__ __volatile__ (
+"1:\t"	PPC_LWARX(%0,0,%2,1) "	# atomic_try_cmpxchg_acquire
\n"
+"	cmpw	0,%0,%3							\n"
+"	bne-	2f							\n"
+"	stwcx.	%4,0,%2							\n"
+"	bne-	1b							\n"
+"\t"	PPC_ACQUIRE_BARRIER "						\n"
+"2:									\n"
+	: "=&r" (r), "+m" (v->counter)
+	: "r" (&v->counter), "r" (o), "r" (new)
+	: "cr0", "memory");
+
+	if (unlikely(r != o))
+		*old = r;
+	return likely(r == o);
+}
+
 /**
  * atomic_fetch_add_unless - add unless the number is a given value
  * @v: pointer of type atomic_t
diff --git a/arch/powerpc/include/asm/qspinlock.h
b/arch/powerpc/include/asm/qspinlock.h
index 997a9a32df77..7091f1ceec3d 100644
--- a/arch/powerpc/include/asm/qspinlock.h
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -26,7 +26,7 @@ static __always_inline void queued_spin_lock(struct qspinlock
*lock)
 {
 	u32 val = 0;
 
-	if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val,
_Q_LOCKED_VAL)))
+	if (likely(atomic_try_cmpxchg_lock(&lock->val, &val,
_Q_LOCKED_VAL)))
 		return;
 
 	queued_spin_lock_slowpath(lock, val);
-- 
2.23.0

Nicholas Piggin

2020-Jul-02 07:48 UTC

head link

[PATCH 8/8] powerpc/64s: remove paravirt from simple spinlocks (RFC only)

RFC until we settle on queued spinlocks for 64s and remove the
option to go back to simple locks. If other sub-archs want to keep
simple spinlocks, the code can be nicely simplified.
---
 arch/powerpc/include/asm/simple_spinlock.h | 61 +-------------------
 arch/powerpc/kvm/book3s_hv_rm_mmu.c        |  6 --
 arch/powerpc/lib/Makefile                  |  4 --
 arch/powerpc/lib/locks.c                   | 65 ----------------------
 4 files changed, 2 insertions(+), 134 deletions(-)
 delete mode 100644 arch/powerpc/lib/locks.c

diff --git a/arch/powerpc/include/asm/simple_spinlock.h
b/arch/powerpc/include/asm/simple_spinlock.h
index e048c041c4a9..5f0980dea001 100644
--- a/arch/powerpc/include/asm/simple_spinlock.h
+++ b/arch/powerpc/include/asm/simple_spinlock.h
@@ -16,23 +16,10 @@
  * (the type definitions are in asm/simple_spinlock_types.h)
  */
 #include <linux/irqflags.h>
-#include <asm/paravirt.h>
-#ifdef CONFIG_PPC64
-#include <asm/paca.h>
-#endif
 #include <asm/synch.h>
 #include <asm/ppc-opcode.h>
 
-#ifdef CONFIG_PPC64
-/* use 0x800000yy when locked, where yy == CPU number */
-#ifdef __BIG_ENDIAN__
-#define LOCK_TOKEN	(*(u32 *)(&get_paca()->lock_token))
-#else
-#define LOCK_TOKEN	(*(u32 *)(&get_paca()->paca_index))
-#endif
-#else
 #define LOCK_TOKEN	1
-#endif
 
 static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
 {
@@ -74,43 +61,14 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock)
 	return __arch_spin_trylock(lock) == 0;
 }
 
-/*
- * On a system with shared processors (that is, where a physical
- * processor is multiplexed between several virtual processors),
- * there is no point spinning on a lock if the holder of the lock
- * isn't currently scheduled on a physical processor.  Instead
- * we detect this situation and ask the hypervisor to give the
- * rest of our timeslice to the lock holder.
- *
- * So that we can tell which virtual processor is holding a lock,
- * we put 0x80000000 | smp_processor_id() in the lock when it is
- * held.  Conveniently, we have a word in the paca that holds this
- * value.
- */
-
-#if defined(CONFIG_PPC_SPLPAR)
-/* We only yield to the hypervisor if we are in shared processor mode */
-void splpar_spin_yield(arch_spinlock_t *lock);
-void splpar_rw_yield(arch_rwlock_t *lock);
-#else /* SPLPAR */
-static inline void splpar_spin_yield(arch_spinlock_t *lock) {};
-static inline void splpar_rw_yield(arch_rwlock_t *lock) {};
-#endif
-
 static inline void spin_yield(arch_spinlock_t *lock)
 {
-	if (is_shared_processor())
-		splpar_spin_yield(lock);
-	else
-		barrier();
+	barrier();
 }
 
 static inline void rw_yield(arch_rwlock_t *lock)
 {
-	if (is_shared_processor())
-		splpar_rw_yield(lock);
-	else
-		barrier();
+	barrier();
 }
 
 static inline void arch_spin_lock(arch_spinlock_t *lock)
@@ -120,8 +78,6 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
 			break;
 		do {
 			HMT_low();
-			if (is_shared_processor())
-				splpar_spin_yield(lock);
 		} while (unlikely(lock->slock != 0));
 		HMT_medium();
 	}
@@ -139,8 +95,6 @@ void arch_spin_lock_flags(arch_spinlock_t *lock, unsigned
long flags)
 		local_irq_restore(flags);
 		do {
 			HMT_low();
-			if (is_shared_processor())
-				splpar_spin_yield(lock);
 		} while (unlikely(lock->slock != 0));
 		HMT_medium();
 		local_irq_restore(flags_dis);
@@ -166,13 +120,7 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
  * read-locks.
  */
 
-#ifdef CONFIG_PPC64
-#define __DO_SIGN_EXTEND	"extsw	%0,%0\n"
-#define WRLOCK_TOKEN		LOCK_TOKEN	/* it's negative */
-#else
-#define __DO_SIGN_EXTEND
 #define WRLOCK_TOKEN		(-1)
-#endif
 
 /*
  * This returns the old value in the lock + 1,
@@ -184,7 +132,6 @@ static inline long __arch_read_trylock(arch_rwlock_t *rw)
 
 	__asm__ __volatile__(
 "1:	" PPC_LWARX(%0,0,%1,1) "\n"
-	__DO_SIGN_EXTEND
 "	addic.		%0,%0,1\n\
 	ble-		2f\n"
 "	stwcx.		%0,0,%1\n\
@@ -227,8 +174,6 @@ static inline void arch_read_lock(arch_rwlock_t *rw)
 			break;
 		do {
 			HMT_low();
-			if (is_shared_processor())
-				splpar_rw_yield(rw);
 		} while (unlikely(rw->lock < 0));
 		HMT_medium();
 	}
@@ -241,8 +186,6 @@ static inline void arch_write_lock(arch_rwlock_t *rw)
 			break;
 		do {
 			HMT_low();
-			if (is_shared_processor())
-				splpar_rw_yield(rw);
 		} while (unlikely(rw->lock != 0));
 		HMT_medium();
 	}
diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 88da2764c1bb..909025083161 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -410,12 +410,6 @@ long kvmppc_h_enter(struct kvm_vcpu *vcpu, unsigned long
flags,
 				 &vcpu->arch.regs.gpr[4]);
 }
 
-#ifdef __BIG_ENDIAN__
-#define LOCK_TOKEN	(*(u32 *)(&get_paca()->lock_token))
-#else
-#define LOCK_TOKEN	(*(u32 *)(&get_paca()->paca_index))
-#endif
-
 static inline int is_mmio_hpte(unsigned long v, unsigned long r)
 {
 	return ((v & HPTE_V_ABSENT) &&
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index d66a645503eb..158e71abc14c 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -41,10 +41,6 @@ obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o
copypage_power7.o \
 obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
 	   memcpy_64.o memcpy_mcsafe_64.o
 
-ifndef CONFIG_PPC_QUEUED_SPINLOCKS
-obj64-$(CONFIG_SMP)	+= locks.o
-endif
-
 obj64-$(CONFIG_ALTIVEC)	+= vmx-helper.o
 obj64-$(CONFIG_KPROBES_SANITY_TEST)	+= test_emulate_step.o \
 					   test_emulate_step_exec_instr.o
diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
deleted file mode 100644
index e35fd1a16992..000000000000
--- a/arch/powerpc/lib/locks.c
+++ /dev/null
@@ -1,65 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * Spin and read/write lock operations.
- *
- * Copyright (C) 2001-2004 Paul Mackerras <paulus at au.ibm.com>, IBM
- * Copyright (C) 2001 Anton Blanchard <anton at au.ibm.com>, IBM
- * Copyright (C) 2002 Dave Engebretsen <engebret at us.ibm.com>, IBM
- *   Rework to support virtual processors
- */
-
-#include <linux/kernel.h>
-#include <linux/spinlock.h>
-#include <linux/export.h>
-#include <linux/smp.h>
-
-/* waiting for a spinlock... */
-#if defined(CONFIG_PPC_SPLPAR)
-#include <asm/hvcall.h>
-#include <asm/smp.h>
-
-void splpar_spin_yield(arch_spinlock_t *lock)
-{
-	unsigned int lock_value, holder_cpu, yield_count;
-
-	lock_value = lock->slock;
-	if (lock_value == 0)
-		return;
-	holder_cpu = lock_value & 0xffff;
-	BUG_ON(holder_cpu >= NR_CPUS);
-
-	yield_count = yield_count_of(holder_cpu);
-	if ((yield_count & 1) == 0)
-		return;		/* virtual cpu is currently running */
-	smp_rmb();
-	if (lock->slock != lock_value)
-		return;		/* something has changed */
-	yield_to_preempted(holder_cpu, yield_count);
-}
-EXPORT_SYMBOL_GPL(splpar_spin_yield);
-
-/*
- * Waiting for a read lock or a write lock on a rwlock...
- * This turns out to be the same for read and write locks, since
- * we only know the holder if it is write-locked.
- */
-void splpar_rw_yield(arch_rwlock_t *rw)
-{
-	int lock_value;
-	unsigned int holder_cpu, yield_count;
-
-	lock_value = rw->lock;
-	if (lock_value >= 0)
-		return;		/* no write lock at present */
-	holder_cpu = lock_value & 0xffff;
-	BUG_ON(holder_cpu >= NR_CPUS);
-
-	yield_count = yield_count_of(holder_cpu);
-	if ((yield_count & 1) == 0)
-		return;		/* virtual cpu is currently running */
-	smp_rmb();
-	if (rw->lock != lock_value)
-		return;		/* something has changed */
-	yield_to_preempted(holder_cpu, yield_count);
-}
-#endif
-- 
2.23.0

Will Deacon

2020-Jul-02 08:02 UTC

head link

[PATCH 5/8] powerpc/64s: implement queued spinlocks and rwlocks

On Thu, Jul 02, 2020 at 05:48:36PM +1000, Nicholas Piggin
wrote:> diff --git a/arch/powerpc/include/asm/qspinlock.h
b/arch/powerpc/include/asm/qspinlock.h
> new file mode 100644
> index 000000000000..f84da77b6bb7
> --- /dev/null
> +++ b/arch/powerpc/include/asm/qspinlock.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_POWERPC_QSPINLOCK_H
> +#define _ASM_POWERPC_QSPINLOCK_H
> +
> +#include <asm-generic/qspinlock_types.h>
> +
> +#define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */
> +
> +#define smp_mb__after_spinlock()   smp_mb()
> +
> +static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
> +{
> +	smp_mb();
> +	return atomic_read(&lock->val);
> +}
Why do you need the smp_mb() here?

Will

Peter Zijlstra

2020-Jul-02 08:28 UTC

head link

[PATCH 2/8] powerpc/pseries: use smp_rmb() in H_CONFER spin yield

On Thu, Jul 02, 2020 at 05:48:33PM +1000, Nicholas Piggin
wrote:> There is no need for rmb(), this allows faster lwsync here.
Since you determined this; I'm thinking you actually understand the
ordering here. How about recording this understanding in a comment?

Also, should the lock->slock load not use READ_ONCE() ?

kernel test robot

2020-Jul-02 16:15 UTC

head link

[PATCH 6/8] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

Hi Nicholas,

I love your patch! Yet something to improve:

[auto build test ERROR on powerpc/next]
[also build test ERROR on tip/locking/core v5.8-rc3 next-20200702]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use  as documented in
https://git-scm.com/docs/git-format-patch]

url:   
https://github.com/0day-ci/linux/commits/Nicholas-Piggin/powerpc-queued-spinlocks-and-rwlocks/20200702-155158
base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
config: powerpc-allyesconfig (attached as .config)
compiler: powerpc64-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross
ARCH=powerpc

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp at intel.com>

All errors (new ones prefixed by >>):

   kernel/locking/lock_events.c:61:16: warning: no previous prototype for
'lockevent_read' [-Wmissing-prototypes]
      61 | ssize_t __weak lockevent_read(struct file *file, char __user
*user_buf,
         |                ^~~~~~~~~~~~~~
   kernel/locking/lock_events.c: In function
'skip_lockevent':>> kernel/locking/lock_events.c:126:12: error: implicit declaration of
function 'pv_is_native_spin_unlock'
[-Werror=implicit-function-declaration]     126 |   pv_on = !pv_is_native_spin_unlock();
         |            ^~~~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/pv_is_native_spin_unlock +126 kernel/locking/lock_events.c

fb346fd9fc081c Waiman Long 2019-04-04   57  
fb346fd9fc081c Waiman Long 2019-04-04   58  /*
fb346fd9fc081c Waiman Long 2019-04-04   59   * The lockevent_read() function can
be overridden.
fb346fd9fc081c Waiman Long 2019-04-04   60   */
fb346fd9fc081c Waiman Long 2019-04-04  @61  ssize_t __weak lockevent_read(struct
file *file, char __user *user_buf,
fb346fd9fc081c Waiman Long 2019-04-04   62  			      size_t count, loff_t *ppos)
fb346fd9fc081c Waiman Long 2019-04-04   63  {
fb346fd9fc081c Waiman Long 2019-04-04   64  	char buf[64];
fb346fd9fc081c Waiman Long 2019-04-04   65  	int cpu, id, len;
fb346fd9fc081c Waiman Long 2019-04-04   66  	u64 sum = 0;
fb346fd9fc081c Waiman Long 2019-04-04   67  
fb346fd9fc081c Waiman Long 2019-04-04   68  	/*
fb346fd9fc081c Waiman Long 2019-04-04   69  	 * Get the counter ID stored in
file->f_inode->i_private
fb346fd9fc081c Waiman Long 2019-04-04   70  	 */
fb346fd9fc081c Waiman Long 2019-04-04   71  	id =
(long)file_inode(file)->i_private;
fb346fd9fc081c Waiman Long 2019-04-04   72  
fb346fd9fc081c Waiman Long 2019-04-04   73  	if (id >= lockevent_num)
fb346fd9fc081c Waiman Long 2019-04-04   74  		return -EBADF;
fb346fd9fc081c Waiman Long 2019-04-04   75  
fb346fd9fc081c Waiman Long 2019-04-04   76  	for_each_possible_cpu(cpu)
fb346fd9fc081c Waiman Long 2019-04-04   77  		sum += per_cpu(lockevents[id],
cpu);
fb346fd9fc081c Waiman Long 2019-04-04   78  	len = snprintf(buf, sizeof(buf) -
1, "%llu\n", sum);
fb346fd9fc081c Waiman Long 2019-04-04   79  
fb346fd9fc081c Waiman Long 2019-04-04   80  	return
simple_read_from_buffer(user_buf, count, ppos, buf, len);
fb346fd9fc081c Waiman Long 2019-04-04   81  }
fb346fd9fc081c Waiman Long 2019-04-04   82  
fb346fd9fc081c Waiman Long 2019-04-04   83  /*
fb346fd9fc081c Waiman Long 2019-04-04   84   * Function to handle write request
fb346fd9fc081c Waiman Long 2019-04-04   85   *
fb346fd9fc081c Waiman Long 2019-04-04   86   * When idx = reset_cnts, reset all
the counts.
fb346fd9fc081c Waiman Long 2019-04-04   87   */
fb346fd9fc081c Waiman Long 2019-04-04   88  static ssize_t
lockevent_write(struct file *file, const char __user *user_buf,
fb346fd9fc081c Waiman Long 2019-04-04   89  			   size_t count, loff_t *ppos)
fb346fd9fc081c Waiman Long 2019-04-04   90  {
fb346fd9fc081c Waiman Long 2019-04-04   91  	int cpu;
fb346fd9fc081c Waiman Long 2019-04-04   92  
fb346fd9fc081c Waiman Long 2019-04-04   93  	/*
fb346fd9fc081c Waiman Long 2019-04-04   94  	 * Get the counter ID stored in
file->f_inode->i_private
fb346fd9fc081c Waiman Long 2019-04-04   95  	 */
fb346fd9fc081c Waiman Long 2019-04-04   96  	if
((long)file_inode(file)->i_private != LOCKEVENT_reset_cnts)
fb346fd9fc081c Waiman Long 2019-04-04   97  		return count;
fb346fd9fc081c Waiman Long 2019-04-04   98  
fb346fd9fc081c Waiman Long 2019-04-04   99  	for_each_possible_cpu(cpu) {
fb346fd9fc081c Waiman Long 2019-04-04  100  		int i;
fb346fd9fc081c Waiman Long 2019-04-04  101  		unsigned long *ptr =
per_cpu_ptr(lockevents, cpu);
fb346fd9fc081c Waiman Long 2019-04-04  102  
fb346fd9fc081c Waiman Long 2019-04-04  103  		for (i = 0 ; i < lockevent_num;
i++)
fb346fd9fc081c Waiman Long 2019-04-04  104  			WRITE_ONCE(ptr[i], 0);
fb346fd9fc081c Waiman Long 2019-04-04  105  	}
fb346fd9fc081c Waiman Long 2019-04-04  106  	return count;
fb346fd9fc081c Waiman Long 2019-04-04  107  }
fb346fd9fc081c Waiman Long 2019-04-04  108  
fb346fd9fc081c Waiman Long 2019-04-04  109  /*
fb346fd9fc081c Waiman Long 2019-04-04  110   * Debugfs data structures
fb346fd9fc081c Waiman Long 2019-04-04  111   */
fb346fd9fc081c Waiman Long 2019-04-04  112  static const struct file_operations
fops_lockevent = {
fb346fd9fc081c Waiman Long 2019-04-04  113  	.read = lockevent_read,
fb346fd9fc081c Waiman Long 2019-04-04  114  	.write = lockevent_write,
fb346fd9fc081c Waiman Long 2019-04-04  115  	.llseek = default_llseek,
fb346fd9fc081c Waiman Long 2019-04-04  116  };
fb346fd9fc081c Waiman Long 2019-04-04  117  
bf20616f46e536 Waiman Long 2019-04-04  118  #ifdef CONFIG_PARAVIRT_SPINLOCKS
bf20616f46e536 Waiman Long 2019-04-04  119  #include <asm/paravirt.h>
bf20616f46e536 Waiman Long 2019-04-04  120  
bf20616f46e536 Waiman Long 2019-04-04  121  static bool __init
skip_lockevent(const char *name)
bf20616f46e536 Waiman Long 2019-04-04  122  {
bf20616f46e536 Waiman Long 2019-04-04  123  	static int pv_on __initdata = -1;
bf20616f46e536 Waiman Long 2019-04-04  124  
bf20616f46e536 Waiman Long 2019-04-04  125  	if (pv_on < 0)
bf20616f46e536 Waiman Long 2019-04-04 @126  		pv_on =
!pv_is_native_spin_unlock();
bf20616f46e536 Waiman Long 2019-04-04  127  	/*
bf20616f46e536 Waiman Long 2019-04-04  128  	 * Skip PV qspinlock events on bare
metal.
bf20616f46e536 Waiman Long 2019-04-04  129  	 */
bf20616f46e536 Waiman Long 2019-04-04  130  	if (!pv_on && !memcmp(name,
"pv_", 3))
bf20616f46e536 Waiman Long 2019-04-04  131  		return true;
bf20616f46e536 Waiman Long 2019-04-04  132  	return false;
bf20616f46e536 Waiman Long 2019-04-04  133  }
bf20616f46e536 Waiman Long 2019-04-04  134  #else
bf20616f46e536 Waiman Long 2019-04-04  135  static inline bool
skip_lockevent(const char *name)
bf20616f46e536 Waiman Long 2019-04-04  136  {
bf20616f46e536 Waiman Long 2019-04-04  137  	return false;
bf20616f46e536 Waiman Long 2019-04-04  138  }
bf20616f46e536 Waiman Long 2019-04-04  139  #endif
bf20616f46e536 Waiman Long 2019-04-04  140  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all at lists.01.org
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Waiman Long

2020-Jul-02 21:01 UTC

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[PATCH 6/8] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

On 7/2/20 3:48 AM, Nicholas Piggin wrote:> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/include/asm/paravirt.h           | 23 ++++++++
>   arch/powerpc/include/asm/qspinlock.h          | 55 +++++++++++++++++++
>   arch/powerpc/include/asm/qspinlock_paravirt.h |  5 ++
>   arch/powerpc/platforms/pseries/Kconfig        |  5 ++
>   arch/powerpc/platforms/pseries/setup.c        |  6 +-
>   include/asm-generic/qspinlock.h               |  2 +
>   6 files changed, 95 insertions(+), 1 deletion(-)
>   create mode 100644 arch/powerpc/include/asm/qspinlock_paravirt.h
>
> diff --git a/arch/powerpc/include/asm/paravirt.h
b/arch/powerpc/include/asm/paravirt.h
> index 7a8546660a63..5fae9dfa6fe9 100644
> --- a/arch/powerpc/include/asm/paravirt.h
> +++ b/arch/powerpc/include/asm/paravirt.h
> @@ -29,6 +29,16 @@ static inline void yield_to_preempted(int cpu, u32
yield_count)
>   {
>   	plpar_hcall_norets(H_CONFER, get_hard_smp_processor_id(cpu),
yield_count);
>   }
> +
> +static inline void prod_cpu(int cpu)
> +{
> +	plpar_hcall_norets(H_PROD, get_hard_smp_processor_id(cpu));
> +}
> +
> +static inline void yield_to_any(void)
> +{
> +	plpar_hcall_norets(H_CONFER, -1, 0);
> +}
>   #else
>   static inline bool is_shared_processor(void)
>   {
> @@ -45,6 +55,19 @@ static inline void yield_to_preempted(int cpu, u32
yield_count)
>   {
>   	___bad_yield_to_preempted(); /* This would be a bug */
>   }
> +
> +extern void ___bad_yield_to_any(void);
> +static inline void yield_to_any(void)
> +{
> +	___bad_yield_to_any(); /* This would be a bug */
> +}
> +
> +extern void ___bad_prod_cpu(void);
> +static inline void prod_cpu(int cpu)
> +{
> +	___bad_prod_cpu(); /* This would be a bug */
> +}
> +
>   #endif
>   
>   #define vcpu_is_preempted vcpu_is_preempted
> diff --git a/arch/powerpc/include/asm/qspinlock.h
b/arch/powerpc/include/asm/qspinlock.h
> index f84da77b6bb7..997a9a32df77 100644
> --- a/arch/powerpc/include/asm/qspinlock.h
> +++ b/arch/powerpc/include/asm/qspinlock.h
> @@ -3,9 +3,36 @@
>   #define _ASM_POWERPC_QSPINLOCK_H
>   
>   #include <asm-generic/qspinlock_types.h>
> +#include <asm/paravirt.h>
>   
>   #define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */
>   
> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
> +extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32
val);
> +extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32
val);
> +
> +static __always_inline void queued_spin_lock_slowpath(struct qspinlock
*lock, u32 val)
> +{
> +	if (!is_shared_processor())
> +		native_queued_spin_lock_slowpath(lock, val);
> +	else
> +		__pv_queued_spin_lock_slowpath(lock, val);
> +}
You may need to match the use of __pv_queued_spin_lock_slowpath() with 
the corresponding __pv_queued_spin_unlock(), e.g.

#define queued_spin_unlock queued_spin_unlock
static inline queued_spin_unlock(struct qspinlock *lock)
{
 ??????? if (!is_shared_processor())
 ??????????????? smp_store_release(&lock->locked, 0);
 ??????? else
 ??????????????? __pv_queued_spin_unlock(lock);
}

Otherwise, pv_kick() will never be called.

Cheers,
Longman

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