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Nicholas Piggin

2020-Jul-24 13:14 UTC

[PATCH v4 0/6] powerpc: queued spinlocks and rwlocks

Updated with everybody's feedback (thanks all), and more performance
results.

What I've found is I might have been measuring the worst load point for
the paravirt case, and by looking at a range of loads it's clear that
queued spinlocks are overall better even on PV, doubly so when you look
at the generally much improved worst case latencies.

I have defaulted it to N even though I'm less concerned about the PV
numbers now, just because I think it needs more stress testing. But
it's very nicely selectable so should be low risk to include.

All in all this is a very cool technology and great results especially
on the big systems but even on smaller ones there are nice gains. Thanks
Waiman and everyone who developed it.

Thanks,
Nick

Nicholas Piggin (6):
  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: implement smp_cond_load_relaxed

 arch/powerpc/Kconfig                          |  15 +
 arch/powerpc/include/asm/Kbuild               |   1 +
 arch/powerpc/include/asm/atomic.h             |  28 ++
 arch/powerpc/include/asm/barrier.h            |  14 +
 arch/powerpc/include/asm/paravirt.h           |  87 +++++
 arch/powerpc/include/asm/qspinlock.h          |  91 ++++++
 arch/powerpc/include/asm/qspinlock_paravirt.h |   7 +
 arch/powerpc/include/asm/simple_spinlock.h    | 288 ++++++++++++++++
 .../include/asm/simple_spinlock_types.h       |  21 ++
 arch/powerpc/include/asm/spinlock.h           | 308 +-----------------
 arch/powerpc/include/asm/spinlock_types.h     |  17 +-
 arch/powerpc/lib/Makefile                     |   3 +
 arch/powerpc/lib/locks.c                      |  12 +-
 arch/powerpc/platforms/pseries/Kconfig        |   9 +-
 arch/powerpc/platforms/pseries/setup.c        |   4 +-
 include/asm-generic/qspinlock.h               |   4 +
 16 files changed, 588 insertions(+), 321 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

-- 
2.23.0

Nicholas Piggin

2020-Jul-24 13:14 UTC

head link

[PATCH v4 1/6] powerpc/pseries: move some PAPR paravirt functions to their own file

These functions will be used by queued spinlock implementation,
and may be useful elsewhere too, so move them out of spinlock.h.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/paravirt.h | 59 +++++++++++++++++++++++++++++
 arch/powerpc/include/asm/spinlock.h | 24 +-----------
 arch/powerpc/lib/locks.c            | 12 +++---
 3 files changed, 66 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..339e8533464b
--- /dev/null
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _ASM_POWERPC_PARAVIRT_H
+#define _ASM_POWERPC_PARAVIRT_H
+
+#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 /* _ASM_POWERPC_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 6440d5943c00..04165b7a163f 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 */
 	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 */
 	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-24 13:14 UTC

head link

[PATCH v4 2/6] 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    | 288 ++++++++++++++++++
 .../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, 311 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..fe6cff7df48e
--- /dev/null
+++ b/arch/powerpc/include/asm/simple_spinlock.h
@@ -0,0 +1,288 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _ASM_POWERPC_SIMPLE_SPINLOCK_H
+#define _ASM_POWERPC_SIMPLE_SPINLOCK_H
+
+/*
+ * 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>
+#include <asm/paca.h>
+#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 /* _ASM_POWERPC_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..0f3cdd8faa95
--- /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 /* _ASM_POWERPC_SIMPLE_SPINLOCK_TYPES_H */
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-24 13:14 UTC

head link

[PATCH v4 3/6] 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.

With this series including subsequent patches, on a 16 socket 1536 thread
POWER9, a stress test such as same-file open/close from all CPUs gets big
speedups, 11620op/s aggregate with simple spinlocks vs 384158op/s (33x
faster), where the difference in throughput between the fastest and slowest
thread goes from 7x to 1.4x.

Thanks to the fast path being identical in terms of atomics and barriers
(after a subsequent optimisation patch), single threaded performance is not
changed (no measurable difference).

On smaller systems, performance and fairness seems to be generally improved.
Using dbench on tmpfs as a test (that starts to run into kernel spinlock
contention), a 2-socket OpenPOWER POWER9 system was tested with bare metal
and KVM guest configurations. Results can be found here:

https://github.com/linuxppc/issues/issues/305#issuecomment-663487453

Observations are:

- Queued spinlocks are equal when contention is insignificant, as expected
  and as measured with microbenchmarks.

- When there is contention, on bare metal queued spinlocks have better
  throughput and max latency at all points.

- When virtualised, queued spinlocks are slightly worse approaching peak
  throughput, but significantly better throughput and max latency at all
  points beyond peak, until queued spinlock maximum latency rises when
  clients are 2x vCPUs.

The regressions haven't been analysed very well yet, there are a lot of
things that can be tuned, particularly the paravirtualised locking, but the
numbers already look like a good net win even on relatively small systems.

Acked-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/Kconfig                      | 15 ++++++++++++++
 arch/powerpc/include/asm/Kbuild           |  1 +
 arch/powerpc/include/asm/qspinlock.h      | 25 +++++++++++++++++++++++
 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, 56 insertions(+)
 create mode 100644 arch/powerpc/include/asm/qspinlock.h

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 9fa23eb320ff..641946052d67 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 +492,19 @@ config HOTPLUG_CPU
 
 	  Say N if you are unsure.
 
+config PPC_QUEUED_SPINLOCKS
+	bool "Queued spinlocks"
+	depends on SMP
+	help
+	  Say Y here to use to use queued spinlocks which give better
+	  scalability and fairness on large SMP and NUMA systems without
+	  harming single threaded performance.
+
+	  This option is currently experimental, the code is more complex
+	  and less tested so it defaults to "N" for the moment.
+
+	  If unsure, say "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..27c2268dfd6c 100644
--- a/arch/powerpc/include/asm/Kbuild
+++ b/arch/powerpc/include/asm/Kbuild
@@ -6,5 +6,6 @@ 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 += 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..c49e33e24edd
--- /dev/null
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -0,0 +1,25 @@
+/* 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)
+{
+	/*
+	 * This barrier was added to simple spinlocks by commit 51d7d5205d338,
+	 * but it should now be possible to remove it, asm arm64 has done with
+	 * commit c6f5d02b6a0f.
+	 */
+	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-24 13:14 UTC

head link

[PATCH v4 4/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

This implements the generic paravirt qspinlocks using H_PROD and H_CONFER to
kick and wait.

This uses an un-directed yield to any CPU rather than the directed yield to
a pre-empted lock holder that paravirtualised simple spinlocks use, that
requires no kick hcall. This is something that could be investigated and
improved in future.

Performance results can be found in the commit which added queued spinlocks.

Acked-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Acked-by: Waiman Long <longman at redhat.com>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/paravirt.h           | 28 ++++++++
 arch/powerpc/include/asm/qspinlock.h          | 66 +++++++++++++++++++
 arch/powerpc/include/asm/qspinlock_paravirt.h |  7 ++
 arch/powerpc/include/asm/spinlock.h           |  4 ++
 arch/powerpc/platforms/pseries/Kconfig        |  9 ++-
 arch/powerpc/platforms/pseries/setup.c        |  4 +-
 include/asm-generic/qspinlock.h               |  2 +
 7 files changed, 118 insertions(+), 2 deletions(-)
 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 339e8533464b..21e5f29ca251 100644
--- a/arch/powerpc/include/asm/paravirt.h
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -28,6 +28,16 @@ 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)
 {
@@ -44,6 +54,19 @@ 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
@@ -56,4 +79,9 @@ static inline bool vcpu_is_preempted(int cpu)
 	return false;
 }
 
+static inline bool pv_is_native_spin_unlock(void)
+{
+     return !is_shared_processor();
+}
+
 #endif /* _ASM_POWERPC_PARAVIRT_H */
diff --git a/arch/powerpc/include/asm/qspinlock.h
b/arch/powerpc/include/asm/qspinlock.h
index c49e33e24edd..f5066f00a08c 100644
--- a/arch/powerpc/include/asm/qspinlock.h
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -3,9 +3,47 @@
 #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);
+extern void __pv_queued_spin_unlock(struct qspinlock *lock);
+
+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);
+}
+
+#define queued_spin_unlock queued_spin_unlock
+static inline void queued_spin_unlock(struct qspinlock *lock)
+{
+	if (!is_shared_processor())
+		smp_store_release(&lock->locked, 0);
+	else
+		__pv_queued_spin_unlock(lock);
+}
+
+#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)
@@ -20,6 +58,34 @@ 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..6b60e7736a47
--- /dev/null
+++ b/arch/powerpc/include/asm/qspinlock_paravirt.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _ASM_POWERPC_QSPINLOCK_PARAVIRT_H
+#define _ASM_POWERPC_QSPINLOCK_PARAVIRT_H
+
+EXPORT_SYMBOL(__pv_queued_spin_unlock);
+
+#endif /* _ASM_POWERPC_QSPINLOCK_PARAVIRT_H */
diff --git a/arch/powerpc/include/asm/spinlock.h
b/arch/powerpc/include/asm/spinlock.h
index 434615f1d761..6ec72282888d 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -10,5 +10,9 @@
 #include <asm/simple_spinlock.h>
 #endif
 
+#ifndef CONFIG_PARAVIRT_SPINLOCKS
+static inline void pv_spinlocks_init(void) { }
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* __ASM_SPINLOCK_H */
diff --git a/arch/powerpc/platforms/pseries/Kconfig
b/arch/powerpc/platforms/pseries/Kconfig
index 24c18362e5ea..5e037df2a3a1 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -25,15 +25,22 @@ config PPC_PSERIES
 	select SWIOTLB
 	default y
 
+config PARAVIRT_SPINLOCKS
+	bool
+
 config PPC_SPLPAR
-	depends on PPC_PSERIES
 	bool "Support for shared-processor logical partitions"
+	depends on PPC_PSERIES
+	select PARAVIRT_SPINLOCKS if PPC_QUEUED_SPINLOCKS
+	default y
 	help
 	  Enabling this option will make the kernel run more efficiently
 	  on logically-partitioned pSeries systems which use shared
 	  processors, that is, which share physical processors between
 	  two or more partitions.
 
+	  Say Y if you are unsure.
+
 config DTL
 	bool "Dispatch Trace Log"
 	depends on PPC_SPLPAR && DEBUG_FS
diff --git a/arch/powerpc/platforms/pseries/setup.c
b/arch/powerpc/platforms/pseries/setup.c
index 2db8469e475f..fa847d1f9d54 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -771,8 +771,10 @@ 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);
+			pv_spinlocks_init();
+		}
 
 		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-24 13:14 UTC

head link

[PATCH v4 5/6] 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 f5066f00a08c..b752d34517b3 100644
--- a/arch/powerpc/include/asm/qspinlock.h
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -37,7 +37,7 @@ 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-24 13:14 UTC

head link

[PATCH v4 6/6] powerpc: implement smp_cond_load_relaxed

This implements smp_cond_load_relaed with the slowpath busy loop using the
preferred SMT priority pattern.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/barrier.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/powerpc/include/asm/barrier.h
b/arch/powerpc/include/asm/barrier.h
index 123adcefd40f..9b4671d38674 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -76,6 +76,20 @@ do {									\
 	___p1;								\
 })
 
+#define smp_cond_load_relaxed(ptr, cond_expr) ({		\
+	typeof(ptr) __PTR = (ptr);				\
+	__unqual_scalar_typeof(*ptr) VAL;			\
+	VAL = READ_ONCE(*__PTR);				\
+	if (unlikely(!(cond_expr))) {				\
+		spin_begin();					\
+		do {						\
+			VAL = READ_ONCE(*__PTR);		\
+		} while (!(cond_expr));				\
+		spin_end();					\
+	}							\
+	(typeof(*ptr))VAL;					\
+})
+
 #ifdef CONFIG_PPC_BOOK3S_64
 #define NOSPEC_BARRIER_SLOT   nop
 #elif defined(CONFIG_PPC_FSL_BOOK3E)
-- 
2.23.0

Waiman Long

2020-Jul-24 21:10 UTC

head link

[PATCH v4 6/6] powerpc: implement smp_cond_load_relaxed

On 7/24/20 9:14 AM, Nicholas Piggin wrote:> This implements smp_cond_load_relaed with the slowpath busy loop using the
Nit: "smp_cond_load_relaxed"

Cheers,
Longman

Waiman Long

2020-Jul-24 21:11 UTC

head link

[PATCH v4 0/6] powerpc: queued spinlocks and rwlocks

On 7/24/20 9:14 AM, Nicholas Piggin wrote:> Updated with everybody's feedback (thanks all), and more performance
> results.
>
> What I've found is I might have been measuring the worst load point for
> the paravirt case, and by looking at a range of loads it's clear that
> queued spinlocks are overall better even on PV, doubly so when you look
> at the generally much improved worst case latencies.
>
> I have defaulted it to N even though I'm less concerned about the PV
> numbers now, just because I think it needs more stress testing. But
> it's very nicely selectable so should be low risk to include.
>
> All in all this is a very cool technology and great results especially
> on the big systems but even on smaller ones there are nice gains. Thanks
> Waiman and everyone who developed it.
>
> Thanks,
> Nick
>
> Nicholas Piggin (6):
>    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: implement smp_cond_load_relaxed
>
>   arch/powerpc/Kconfig                          |  15 +
>   arch/powerpc/include/asm/Kbuild               |   1 +
>   arch/powerpc/include/asm/atomic.h             |  28 ++
>   arch/powerpc/include/asm/barrier.h            |  14 +
>   arch/powerpc/include/asm/paravirt.h           |  87 +++++
>   arch/powerpc/include/asm/qspinlock.h          |  91 ++++++
>   arch/powerpc/include/asm/qspinlock_paravirt.h |   7 +
>   arch/powerpc/include/asm/simple_spinlock.h    | 288 ++++++++++++++++
>   .../include/asm/simple_spinlock_types.h       |  21 ++
>   arch/powerpc/include/asm/spinlock.h           | 308 +-----------------
>   arch/powerpc/include/asm/spinlock_types.h     |  17 +-
>   arch/powerpc/lib/Makefile                     |   3 +
>   arch/powerpc/lib/locks.c                      |  12 +-
>   arch/powerpc/platforms/pseries/Kconfig        |   9 +-
>   arch/powerpc/platforms/pseries/setup.c        |   4 +-
>   include/asm-generic/qspinlock.h               |   4 +
>   16 files changed, 588 insertions(+), 321 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
>That patch series looks good to me. Thanks for working on this.

For the series,

Acked-by: Waiman Long <longman at redhat.com>

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Linux Virtualization - Jul 2020 - [PATCH v4 0/6] powerpc: queued spinlocks and rwlocks

[PATCH v4 0/6] powerpc: queued spinlocks and rwlocks

[PATCH v4 1/6] powerpc/pseries: move some PAPR paravirt functions to their own file

[PATCH v4 2/6] powerpc: move spinlock implementation to simple_spinlock

[PATCH v4 3/6] powerpc/64s: implement queued spinlocks and rwlocks

[PATCH v4 4/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

[PATCH v4 5/6] powerpc/qspinlock: optimised atomic_try_cmpxchg_lock that adds the lock hint

[PATCH v4 6/6] powerpc: implement smp_cond_load_relaxed

[PATCH v4 6/6] powerpc: implement smp_cond_load_relaxed

[PATCH v4 0/6] powerpc: queued spinlocks and rwlocks

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