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Pan Xinhui

2016-Oct-20 21:27 UTC

[PATCH v5 0/9] implement vcpu preempted check

change from v4:
	spilt x86 kvm vcpu preempted check into two patches.
	add documentation patch.
	add x86 vcpu preempted check patch under xen
	add s390 vcpu preempted check patch 
change from v3:
	add x86 vcpu preempted check patch
change from v2:
	no code change, fix typos, update some comments
change from v1:
	a simplier definition of default vcpu_is_preempted
	skip mahcine type check on ppc, and add config. remove dedicated macro.
	add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. 
	add more comments
	thanks boqun and Peter's suggestion.

This patch set aims to fix lock holder preemption issues.

test-case:
perf record -a perf bench sched messaging -g 400 -p && perf report

18.09%  sched-messaging  [kernel.vmlinux]  [k] osq_lock
12.28%  sched-messaging  [kernel.vmlinux]  [k] rwsem_spin_on_owner
 5.27%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
 3.89%  sched-messaging  [kernel.vmlinux]  [k] wait_consider_task
 3.64%  sched-messaging  [kernel.vmlinux]  [k] _raw_write_lock_irq
 3.41%  sched-messaging  [kernel.vmlinux]  [k] mutex_spin_on_owner.is
 2.49%  sched-messaging  [kernel.vmlinux]  [k] system_call

We introduce interface bool vcpu_is_preempted(int cpu) and use it in some spin
loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner.
These spin_on_onwer variant also cause rcu stall before we apply this patch set

We also have observed some performace improvements in uninx benchmark tests.

PPC test result:
1 copy - 0.94%
2 copy - 7.17%
4 copy - 11.9%
8 copy -  3.04%
16 copy - 15.11%

details below:
Without patch:

1 copy - File Write 4096 bufsize 8000 maxblocks      2188223.0 KBps  (30.0 s, 1
samples)
2 copy - File Write 4096 bufsize 8000 maxblocks      1804433.0 KBps  (30.0 s, 1
samples)
4 copy - File Write 4096 bufsize 8000 maxblocks      1237257.0 KBps  (30.0 s, 1
samples)
8 copy - File Write 4096 bufsize 8000 maxblocks      1032658.0 KBps  (30.0 s, 1
samples)
16 copy - File Write 4096 bufsize 8000 maxblocks       768000.0 KBps  (30.1 s, 1
samples)

With patch: 

1 copy - File Write 4096 bufsize 8000 maxblocks      2209189.0 KBps  (30.0 s, 1
samples)
2 copy - File Write 4096 bufsize 8000 maxblocks      1943816.0 KBps  (30.0 s, 1
samples)
4 copy - File Write 4096 bufsize 8000 maxblocks      1405591.0 KBps  (30.0 s, 1
samples)
8 copy - File Write 4096 bufsize 8000 maxblocks      1065080.0 KBps  (30.0 s, 1
samples)
16 copy - File Write 4096 bufsize 8000 maxblocks       904762.0 KBps  (30.0 s, 1
samples)

X86 test result:
	test-case			after-patch	  before-patch
Execl Throughput                       |    18307.9 lps  |    11701.6 lps 
File Copy 1024 bufsize 2000 maxblocks  |  1352407.3 KBps |   790418.9 KBps
File Copy 256 bufsize 500 maxblocks    |   367555.6 KBps |   222867.7 KBps
File Copy 4096 bufsize 8000 maxblocks  |  3675649.7 KBps |  1780614.4 KBps
Pipe Throughput                        | 11872208.7 lps  | 11855628.9 lps 
Pipe-based Context Switching           |  1495126.5 lps  |  1490533.9 lps 
Process Creation                       |    29881.2 lps  |    28572.8 lps 
Shell Scripts (1 concurrent)           |    23224.3 lpm  |    22607.4 lpm 
Shell Scripts (8 concurrent)           |     3531.4 lpm  |     3211.9 lpm 
System Call Overhead                   | 10385653.0 lps  | 10419979.0 lps 

Christian Borntraeger (1):
  s390/spinlock: Provide vcpu_is_preempted

Juergen Gross (1):
  x86, xen: support vcpu preempted check

Pan Xinhui (7):
  kernel/sched: introduce vcpu preempted check interface
  locking/osq: Drop the overload of osq_lock()
  kernel/locking: Drop the overload of {mutex,rwsem}_spin_on_owner
  powerpc/spinlock: support vcpu preempted check
  x86, paravirt: Add interface to support kvm/xen vcpu preempted check
  x86, kvm: support vcpu preempted check
  Documentation: virtual: kvm: Support vcpu preempted check

 Documentation/virtual/kvm/msr.txt     |  8 +++++++-
 arch/powerpc/include/asm/spinlock.h   |  8 ++++++++
 arch/s390/include/asm/spinlock.h      |  8 ++++++++
 arch/s390/kernel/smp.c                |  9 +++++++--
 arch/s390/lib/spinlock.c              | 25 ++++++++-----------------
 arch/x86/include/asm/paravirt_types.h |  2 ++
 arch/x86/include/asm/spinlock.h       |  8 ++++++++
 arch/x86/include/uapi/asm/kvm_para.h  |  3 ++-
 arch/x86/kernel/kvm.c                 | 12 ++++++++++++
 arch/x86/kernel/paravirt-spinlocks.c  |  6 ++++++
 arch/x86/kvm/x86.c                    | 18 ++++++++++++++++++
 arch/x86/xen/spinlock.c               |  3 ++-
 include/linux/sched.h                 | 12 ++++++++++++
 kernel/locking/mutex.c                | 15 +++++++++++++--
 kernel/locking/osq_lock.c             | 10 +++++++++-
 kernel/locking/rwsem-xadd.c           | 16 +++++++++++++---
 16 files changed, 135 insertions(+), 28 deletions(-)

-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 1/9] kernel/sched: introduce vcpu preempted check interface

This patch support to fix lock holder preemption issue.

For kernel users, we could use bool vcpu_is_preempted(int cpu) to detech if
one vcpu is preempted or not.

The default implementation is a macro defined by false. So compiler can
wrap it out if arch dose not support such vcpu pteempted check.

Suggested-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
Tested-by: Juergen Gross <jgross at suse.com>
---
 include/linux/sched.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 348f51b..44c1ce7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3506,6 +3506,18 @@ static inline void set_task_cpu(struct task_struct *p,
unsigned int cpu)
 
 #endif /* CONFIG_SMP */
 
+/*
+ * In order to deal with a various lock holder preemption issues provide an
+ * interface to see if a vCPU is currently running or not.
+ *
+ * This allows us to terminate optimistic spin loops and block, analogous to
+ * the native optimistic spin heuristic of testing if the lock owner task is
+ * running or not.
+ */
+#ifndef vcpu_is_preempted
+#define vcpu_is_preempted(cpu)	false
+#endif
+
 extern long sched_setaffinity(pid_t pid, const struct cpumask *new_mask);
 extern long sched_getaffinity(pid_t pid, struct cpumask *mask);
 
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 2/9] locking/osq: Drop the overload of osq_lock()

An over-committed guest with more vCPUs than pCPUs has a heavy overload in
osq_lock().

This is because vCPU A hold the osq lock and yield out, vCPU B wait per_cpu
node->locked to be set. IOW, vCPU B wait vCPU A to run and unlock the osq
lock.

Kernel has an interface bool vcpu_is_preempted(int cpu) to see if a vCPU is
currently running or not. So break the spin loops on true condition.

test case:
perf record -a perf bench sched messaging -g 400 -p && perf report

before patch:
18.09%  sched-messaging  [kernel.vmlinux]  [k] osq_lock
12.28%  sched-messaging  [kernel.vmlinux]  [k] rwsem_spin_on_owner
 5.27%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
 3.89%  sched-messaging  [kernel.vmlinux]  [k] wait_consider_task
 3.64%  sched-messaging  [kernel.vmlinux]  [k] _raw_write_lock_irq
 3.41%  sched-messaging  [kernel.vmlinux]  [k] mutex_spin_on_owner.is
 2.49%  sched-messaging  [kernel.vmlinux]  [k] system_call

after patch:
20.68%  sched-messaging  [kernel.vmlinux]  [k] mutex_spin_on_owner
 8.45%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
 4.12%  sched-messaging  [kernel.vmlinux]  [k] system_call
 3.01%  sched-messaging  [kernel.vmlinux]  [k] system_call_common
 2.83%  sched-messaging  [kernel.vmlinux]  [k] copypage_power7
 2.64%  sched-messaging  [kernel.vmlinux]  [k] rwsem_spin_on_owner
 2.00%  sched-messaging  [kernel.vmlinux]  [k] osq_lock

Suggested-by: Boqun Feng <boqun.feng at gmail.com>
Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
Tested-by: Juergen Gross <jgross at suse.com>
---
 kernel/locking/osq_lock.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 05a3785..39d1385 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -21,6 +21,11 @@ static inline int encode_cpu(int cpu_nr)
 	return cpu_nr + 1;
 }
 
+static inline int node_cpu(struct optimistic_spin_node *node)
+{
+	return node->cpu - 1;
+}
+
 static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val)
 {
 	int cpu_nr = encoded_cpu_val - 1;
@@ -118,8 +123,11 @@ bool osq_lock(struct optimistic_spin_queue *lock)
 	while (!READ_ONCE(node->locked)) {
 		/*
 		 * If we need to reschedule bail... so we can block.
+		 * Use vcpu_is_preempted to detech lock holder preemption issue
+		 * and break. vcpu_is_preempted is a macro defined by false if
+		 * arch does not support vcpu preempted check,
 		 */
-		if (need_resched())
+		if (need_resched() || vcpu_is_preempted(node_cpu(node->prev)))
 			goto unqueue;
 
 		cpu_relax_lowlatency();
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 3/9] kernel/locking: Drop the overload of {mutex, rwsem}_spin_on_owner

An over-committed guest with more vCPUs than pCPUs has a heavy overload in
the two spin_on_owner. This blames on the lock holder preemption issue.

Kernel has an interface bool vcpu_is_preempted(int cpu) to see if a vCPU is
currently running or not. So break the spin loops on true condition.

test-case:
perf record -a perf bench sched messaging -g 400 -p && perf report

before patch:
20.68%  sched-messaging  [kernel.vmlinux]  [k] mutex_spin_on_owner
 8.45%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
 4.12%  sched-messaging  [kernel.vmlinux]  [k] system_call
 3.01%  sched-messaging  [kernel.vmlinux]  [k] system_call_common
 2.83%  sched-messaging  [kernel.vmlinux]  [k] copypage_power7
 2.64%  sched-messaging  [kernel.vmlinux]  [k] rwsem_spin_on_owner
 2.00%  sched-messaging  [kernel.vmlinux]  [k] osq_lock

after patch:
 9.99%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
 5.28%  sched-messaging  [unknown]         [H] 0xc0000000000768e0
 4.27%  sched-messaging  [kernel.vmlinux]  [k] __copy_tofrom_user_power7
 3.77%  sched-messaging  [kernel.vmlinux]  [k] copypage_power7
 3.24%  sched-messaging  [kernel.vmlinux]  [k] _raw_write_lock_irq
 3.02%  sched-messaging  [kernel.vmlinux]  [k] system_call
 2.69%  sched-messaging  [kernel.vmlinux]  [k] wait_consider_task

Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
Tested-by: Juergen Gross <jgross at suse.com>
---
 kernel/locking/mutex.c      | 15 +++++++++++++--
 kernel/locking/rwsem-xadd.c | 16 +++++++++++++---
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index a70b90d..82108f5 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -236,7 +236,13 @@ bool mutex_spin_on_owner(struct mutex *lock, struct
task_struct *owner)
 		 */
 		barrier();
 
-		if (!owner->on_cpu || need_resched()) {
+		/*
+		 * Use vcpu_is_preempted to detech lock holder preemption issue
+		 * and break. vcpu_is_preempted is a macro defined by false if
+		 * arch does not support vcpu preempted check,
+		 */
+		if (!owner->on_cpu || need_resched() ||
+				vcpu_is_preempted(task_cpu(owner))) {
 			ret = false;
 			break;
 		}
@@ -261,8 +267,13 @@ static inline int mutex_can_spin_on_owner(struct mutex
*lock)
 
 	rcu_read_lock();
 	owner = READ_ONCE(lock->owner);
+
+	/*
+	 * As lock holder preemption issue, we both skip spinning if task is not
+	 * on cpu or its cpu is preempted
+	 */
 	if (owner)
-		retval = owner->on_cpu;
+		retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
 	rcu_read_unlock();
 	/*
 	 * if lock->owner is not set, the mutex owner may have just acquired
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 2337b4b..0897179 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -336,7 +336,11 @@ static inline bool rwsem_can_spin_on_owner(struct
rw_semaphore *sem)
 		goto done;
 	}
 
-	ret = owner->on_cpu;
+	/*
+	 * As lock holder preemption issue, we both skip spinning if task is not
+	 * on cpu or its cpu is preempted
+	 */
+	ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
 done:
 	rcu_read_unlock();
 	return ret;
@@ -362,8 +366,14 @@ static noinline bool rwsem_spin_on_owner(struct
rw_semaphore *sem)
 		 */
 		barrier();
 
-		/* abort spinning when need_resched or owner is not running */
-		if (!owner->on_cpu || need_resched()) {
+		/*
+		 * abort spinning when need_resched or owner is not running or
+		 * owner's cpu is preempted. vcpu_is_preempted is a macro
+		 * defined by false if arch does not support vcpu preempted
+		 * check
+		 */
+		if (!owner->on_cpu || need_resched() ||
+				vcpu_is_preempted(task_cpu(owner))) {
 			rcu_read_unlock();
 			return false;
 		}
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 4/9] powerpc/spinlock: support vcpu preempted check

This is to fix some lock holder preemption issues. Some other locks
implementation do a spin loop before acquiring the lock itself.
Currently kernel has an interface of bool vcpu_is_preempted(int cpu). It
takes the cpu as parameter and return true if the cpu is preempted. Then
kernel can break the spin loops upon on the retval of vcpu_is_preempted.

As kernel has used this interface, So lets support it.

Only pSeries need support it. And the fact is powerNV are built into
same kernel image with pSeries. So we need return false if we are runnig
as powerNV. The another fact is that lppaca->yiled_count keeps zero on
powerNV. So we can just skip the machine type check.

Suggested-by: Boqun Feng <boqun.feng at gmail.com>
Suggested-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/spinlock.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/include/asm/spinlock.h
b/arch/powerpc/include/asm/spinlock.h
index abb6b0f..f4a9524 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -52,6 +52,14 @@
 #define SYNC_IO
 #endif
 
+#ifdef CONFIG_PPC_PSERIES
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+	return !!(be32_to_cpu(lppaca_of(cpu).yield_count) & 1);
+}
+#endif
+
 #if defined(CONFIG_PPC_SPLPAR)
 /* We only yield to the hypervisor if we are in shared processor mode */
 #define SHARED_PROCESSOR (lppaca_shared_proc(local_paca->lppaca_ptr))
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 5/9] x86, paravirt: Add interface to support kvm/xen vcpu preempted check

This is to fix some lock holder preemption issues. Some other locks
implementation do a spin loop before acquiring the lock itself.
Currently kernel has an interface of bool vcpu_is_preempted(int cpu). It
takes the cpu as parameter and return true if the cpu is preempted.
Then kernel can break the spin loops upon on the retval of
vcpu_is_preempted.

As kernel has used this interface, So lets support it.

To deal with kernel and kvm/xen, add vcpu_is_preempted into struct
pv_lock_ops.

Then kvm or xen could provide their own implementation to support
vcpu_is_preempted.

Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
---
 arch/x86/include/asm/paravirt_types.h | 2 ++
 arch/x86/include/asm/spinlock.h       | 8 ++++++++
 arch/x86/kernel/paravirt-spinlocks.c  | 6 ++++++
 3 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 0f400c0..38c3bb7 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -310,6 +310,8 @@ struct pv_lock_ops {
 
 	void (*wait)(u8 *ptr, u8 val);
 	void (*kick)(int cpu);
+
+	bool (*vcpu_is_preempted)(int cpu);
 };
 
 /* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 921bea7..0526f59 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -26,6 +26,14 @@
 extern struct static_key paravirt_ticketlocks_enabled;
 static __always_inline bool static_key_false(struct static_key *key);
 
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+	return pv_lock_ops.vcpu_is_preempted(cpu);
+}
+#endif
+
 #include <asm/qspinlock.h>
 
 /*
diff --git a/arch/x86/kernel/paravirt-spinlocks.c
b/arch/x86/kernel/paravirt-spinlocks.c
index 2c55a00..2f204dd 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -21,12 +21,18 @@ bool pv_is_native_spin_unlock(void)
 		__raw_callee_save___native_queued_spin_unlock;
 }
 
+static bool native_vcpu_is_preempted(int cpu)
+{
+	return 0;
+}
+
 struct pv_lock_ops pv_lock_ops = {
 #ifdef CONFIG_SMP
 	.queued_spin_lock_slowpath = native_queued_spin_lock_slowpath,
 	.queued_spin_unlock = PV_CALLEE_SAVE(__native_queued_spin_unlock),
 	.wait = paravirt_nop,
 	.kick = paravirt_nop,
+	.vcpu_is_preempted = native_vcpu_is_preempted,
 #endif /* SMP */
 };
 EXPORT_SYMBOL(pv_lock_ops);
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 6/9] x86, kvm: support vcpu preempted check

Support the vcpu_is_preempted() functionality under KVM. This will
enhance lock performance on overcommitted hosts (more runnable vcpus
than physical cpus in the system) as doing busy waits for preempted
vcpus will hurt system performance far worse than early yielding.

Use one field of struct kvm_steal_time to indicate that if one vcpu
is running or not.

unix benchmark result:
host:  kernel 4.8.1, i5-4570, 4 cpus
guest: kernel 4.8.1, 8 vcpus

        test-case                       after-patch       before-patch
Execl Throughput                       |    18307.9 lps  |    11701.6 lps
File Copy 1024 bufsize 2000 maxblocks  |  1352407.3 KBps |   790418.9 KBps
File Copy 256 bufsize 500 maxblocks    |   367555.6 KBps |   222867.7 KBps
File Copy 4096 bufsize 8000 maxblocks  |  3675649.7 KBps |  1780614.4 KBps
Pipe Throughput                        | 11872208.7 lps  | 11855628.9 lps
Pipe-based Context Switching           |  1495126.5 lps  |  1490533.9 lps
Process Creation                       |    29881.2 lps  |    28572.8 lps
Shell Scripts (1 concurrent)           |    23224.3 lpm  |    22607.4 lpm
Shell Scripts (8 concurrent)           |     3531.4 lpm  |     3211.9 lpm
System Call Overhead                   | 10385653.0 lps  | 10419979.0 lps

Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
---
 arch/x86/include/uapi/asm/kvm_para.h |  3 ++-
 arch/x86/kernel/kvm.c                | 12 ++++++++++++
 arch/x86/kvm/x86.c                   | 18 ++++++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h
b/arch/x86/include/uapi/asm/kvm_para.h
index 94dc8ca..b3fec56 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -45,7 +45,8 @@ struct kvm_steal_time {
 	__u64 steal;
 	__u32 version;
 	__u32 flags;
-	__u32 pad[12];
+	__u8 preempted;
+	__u32 pad[11];
 };
 
 #define KVM_STEAL_ALIGNMENT_BITS 5
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index edbbfc8..0b48dd2 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -415,6 +415,15 @@ void kvm_disable_steal_time(void)
 	wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
 }
 
+static bool kvm_vcpu_is_preempted(int cpu)
+{
+	struct kvm_steal_time *src;
+
+	src = &per_cpu(steal_time, cpu);
+
+	return !!src->preempted;
+}
+
 #ifdef CONFIG_SMP
 static void __init kvm_smp_prepare_boot_cpu(void)
 {
@@ -471,6 +480,9 @@ void __init kvm_guest_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
 		has_steal_clock = 1;
 		pv_time_ops.steal_clock = kvm_steal_clock;
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+		pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted;
+#endif
 	}
 
 	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c633de..a627537 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2057,6 +2057,8 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 		&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
 		return;
 
+	vcpu->arch.st.steal.preempted = 0;
+
 	if (vcpu->arch.st.steal.version & 1)
 		vcpu->arch.st.steal.version += 1;  /* first time write, random junk */
 
@@ -2810,8 +2812,24 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
 }
 
+static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
+{
+	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
+		return;
+
+	if (unlikely(kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
+			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
+		return;
+
+	vcpu->arch.st.steal.preempted = 1;
+
+	kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
+			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
+}
+
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	kvm_steal_time_set_preempted(vcpu);
 	kvm_x86_ops->vcpu_put(vcpu);
 	kvm_put_guest_fpu(vcpu);
 	vcpu->arch.last_host_tsc = rdtsc();
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 7/9] x86, xen: support vcpu preempted check

From: Juergen Gross <jgross at suse.com>

Support the vcpu_is_preempted() functionality under Xen. This will
enhance lock performance on overcommitted hosts (more runnable vcpus
than physical cpus in the system) as doing busy waits for preempted
vcpus will hurt system performance far worse than early yielding.

A quick test (4 vcpus on 1 physical cpu doing a parallel build job
with "make -j 8") reduced system time by about 5% with this patch.

Signed-off-by: Juergen Gross <jgross at suse.com>
Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
---
 arch/x86/xen/spinlock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 3d6e006..74756bb 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -114,7 +114,6 @@ void xen_uninit_lock_cpu(int cpu)
 	per_cpu(irq_name, cpu) = NULL;
 }
 
-
 /*
  * Our init of PV spinlocks is split in two init functions due to us
  * using paravirt patching and jump labels patching and having to do
@@ -137,6 +136,8 @@ void __init xen_init_spinlocks(void)
 	pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
 	pv_lock_ops.wait = xen_qlock_wait;
 	pv_lock_ops.kick = xen_qlock_kick;
+
+	pv_lock_ops.vcpu_is_preempted = xen_vcpu_stolen;
 }
 
 /*
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 8/9] s390/spinlock: Provide vcpu_is_preempted

From: Christian Borntraeger <borntraeger at de.ibm.com>

this implements the s390 backend for commit
"kernel/sched: introduce vcpu preempted check interface"
by reworking the existing smp_vcpu_scheduled into
arch_vcpu_is_preempted. We can then also get rid of the
local cpu_is_preempted function by moving the
CIF_ENABLED_WAIT test into arch_vcpu_is_preempted.

Signed-off-by: Christian Borntraeger <borntraeger at de.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens at de.ibm.com>
---
 arch/s390/include/asm/spinlock.h |  8 ++++++++
 arch/s390/kernel/smp.c           |  9 +++++++--
 arch/s390/lib/spinlock.c         | 25 ++++++++-----------------
 3 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/arch/s390/include/asm/spinlock.h b/arch/s390/include/asm/spinlock.h
index 7e9e09f..7ecd890 100644
--- a/arch/s390/include/asm/spinlock.h
+++ b/arch/s390/include/asm/spinlock.h
@@ -23,6 +23,14 @@ _raw_compare_and_swap(unsigned int *lock, unsigned int old,
unsigned int new)
 	return __sync_bool_compare_and_swap(lock, old, new);
 }
 
+#ifndef CONFIG_SMP
+static inline bool arch_vcpu_is_preempted(int cpu) { return false; }
+#else
+bool arch_vcpu_is_preempted(int cpu);
+#endif
+
+#define vcpu_is_preempted arch_vcpu_is_preempted
+
 /*
  * Simple spin lock operations.  There are two variants, one clears IRQ's
  * on the local processor, one does not.
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 35531fe..b988ed1 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -368,10 +368,15 @@ int smp_find_processor_id(u16 address)
 	return -1;
 }
 
-int smp_vcpu_scheduled(int cpu)
+bool arch_vcpu_is_preempted(int cpu)
 {
-	return pcpu_running(pcpu_devices + cpu);
+	if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
+		return false;
+	if (pcpu_running(pcpu_devices + cpu))
+		return false;
+	return true;
 }
+EXPORT_SYMBOL(arch_vcpu_is_preempted);
 
 void smp_yield_cpu(int cpu)
 {
diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index e5f50a7..e48a48e 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -37,15 +37,6 @@ static inline void _raw_compare_and_delay(unsigned int *lock,
unsigned int old)
 	asm(".insn rsy,0xeb0000000022,%0,0,%1" : : "d" (old),
"Q" (*lock));
 }
 
-static inline int cpu_is_preempted(int cpu)
-{
-	if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
-		return 0;
-	if (smp_vcpu_scheduled(cpu))
-		return 0;
-	return 1;
-}
-
 void arch_spin_lock_wait(arch_spinlock_t *lp)
 {
 	unsigned int cpu = SPINLOCK_LOCKVAL;
@@ -62,7 +53,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
 			continue;
 		}
 		/* First iteration: check if the lock owner is running. */
-		if (first_diag && cpu_is_preempted(~owner)) {
+		if (first_diag && arch_vcpu_is_preempted(~owner)) {
 			smp_yield_cpu(~owner);
 			first_diag = 0;
 			continue;
@@ -81,7 +72,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
 		 * yield the CPU unconditionally. For LPAR rely on the
 		 * sense running status.
 		 */
-		if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {
+		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {
 			smp_yield_cpu(~owner);
 			first_diag = 0;
 		}
@@ -108,7 +99,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned
long flags)
 			continue;
 		}
 		/* Check if the lock owner is running. */
-		if (first_diag && cpu_is_preempted(~owner)) {
+		if (first_diag && arch_vcpu_is_preempted(~owner)) {
 			smp_yield_cpu(~owner);
 			first_diag = 0;
 			continue;
@@ -127,7 +118,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned
long flags)
 		 * yield the CPU unconditionally. For LPAR rely on the
 		 * sense running status.
 		 */
-		if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {
+		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {
 			smp_yield_cpu(~owner);
 			first_diag = 0;
 		}
@@ -165,7 +156,7 @@ void _raw_read_lock_wait(arch_rwlock_t *rw)
 	owner = 0;
 	while (1) {
 		if (count-- <= 0) {
-			if (owner && cpu_is_preempted(~owner))
+			if (owner && arch_vcpu_is_preempted(~owner))
 				smp_yield_cpu(~owner);
 			count = spin_retry;
 		}
@@ -211,7 +202,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int
prev)
 	owner = 0;
 	while (1) {
 		if (count-- <= 0) {
-			if (owner && cpu_is_preempted(~owner))
+			if (owner && arch_vcpu_is_preempted(~owner))
 				smp_yield_cpu(~owner);
 			count = spin_retry;
 		}
@@ -241,7 +232,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
 	owner = 0;
 	while (1) {
 		if (count-- <= 0) {
-			if (owner && cpu_is_preempted(~owner))
+			if (owner && arch_vcpu_is_preempted(~owner))
 				smp_yield_cpu(~owner);
 			count = spin_retry;
 		}
@@ -285,7 +276,7 @@ void arch_lock_relax(unsigned int cpu)
 {
 	if (!cpu)
 		return;
-	if (MACHINE_IS_LPAR && !cpu_is_preempted(~cpu))
+	if (MACHINE_IS_LPAR && !arch_vcpu_is_preempted(~cpu))
 		return;
 	smp_yield_cpu(~cpu);
 }
-- 
2.4.11

Pan Xinhui

2016-Oct-20 21:27 UTC

head link

[PATCH v5 9/9] Documentation: virtual: kvm: Support vcpu preempted check

Commit ("x86, kvm: support vcpu preempted check") add one field
"__u8
preempted" into struct kvm_steal_time. This field tells if one vcpu is
running or not.

It is zero if 1) some old KVM deos not support this filed. 2) the vcpu is
preempted. Other values means the vcpu has been preempted.

Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
---
 Documentation/virtual/kvm/msr.txt | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/Documentation/virtual/kvm/msr.txt
b/Documentation/virtual/kvm/msr.txt
index 2a71c8f..3376f13 100644
--- a/Documentation/virtual/kvm/msr.txt
+++ b/Documentation/virtual/kvm/msr.txt
@@ -208,7 +208,8 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
 		__u64 steal;
 		__u32 version;
 		__u32 flags;
-		__u32 pad[12];
+		__u8  preempted;
+		__u32 pad[11];
 	}
 
 	whose data will be filled in by the hypervisor periodically. Only one
@@ -232,6 +233,11 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
 		nanoseconds. Time during which the vcpu is idle, will not be
 		reported as steal time.
 
+		preempted: indicate the VCPU who owns this struct is running or
+		not. Non-zero values mean the VCPU has been preempted. Zero
+		means the VCPU is not preempted. NOTE, it is always zero if the
+		the hypervisor doesn't support this field.
+
 MSR_KVM_EOI_EN: 0x4b564d04
 	data: Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0
 	when disabled.  Bit 1 is reserved and must be zero.  When PV end of
-- 
2.4.11

Boqun Feng

2016-Oct-21 01:23 UTC

head link

[PATCH v5 9/9] Documentation: virtual: kvm: Support vcpu preempted check

On Thu, Oct 20, 2016 at 05:27:54PM -0400, Pan Xinhui
wrote:> Commit ("x86, kvm: support vcpu preempted check") add one field
"__u8
> preempted" into struct kvm_steal_time. This field tells if one vcpu is
> running or not.
> 
> It is zero if 1) some old KVM deos not support this filed. 2) the vcpu is
> preempted. Other values means the vcpu has been preempted.  ^^^^^^^^^
s/preempted/not preempted

And better to fix other typos in the commit log ;-)
Maybe you can try aspell? That works for me.

Regards,
Boqun
> 
> Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
> ---
>  Documentation/virtual/kvm/msr.txt | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virtual/kvm/msr.txt
b/Documentation/virtual/kvm/msr.txt
> index 2a71c8f..3376f13 100644
> --- a/Documentation/virtual/kvm/msr.txt
> +++ b/Documentation/virtual/kvm/msr.txt
> @@ -208,7 +208,8 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
>  		__u64 steal;
>  		__u32 version;
>  		__u32 flags;
> -		__u32 pad[12];
> +		__u8  preempted;
> +		__u32 pad[11];
>  	}
>  
>  	whose data will be filled in by the hypervisor periodically. Only one
> @@ -232,6 +233,11 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
>  		nanoseconds. Time during which the vcpu is idle, will not be
>  		reported as steal time.
>  
> +		preempted: indicate the VCPU who owns this struct is running or
> +		not. Non-zero values mean the VCPU has been preempted. Zero
> +		means the VCPU is not preempted. NOTE, it is always zero if the
> +		the hypervisor doesn't support this field.
> +
>  MSR_KVM_EOI_EN: 0x4b564d04
>  	data: Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0
>  	when disabled.  Bit 1 is reserved and must be zero.  When PV end of
> -- 
> 2.4.11
> -------------- next part --------------
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Juergen Gross

2016-Oct-21 05:08 UTC

head link

[PATCH v5 7/9] x86, xen: support vcpu preempted check

Corrected xen-devel mailing list address, added other Xen maintainers

On 20/10/16 23:27, Pan Xinhui wrote:> From: Juergen Gross <jgross at suse.com>
> 
> Support the vcpu_is_preempted() functionality under Xen. This will
> enhance lock performance on overcommitted hosts (more runnable vcpus
> than physical cpus in the system) as doing busy waits for preempted
> vcpus will hurt system performance far worse than early yielding.
> 
> A quick test (4 vcpus on 1 physical cpu doing a parallel build job
> with "make -j 8") reduced system time by about 5% with this
patch.
> 
> Signed-off-by: Juergen Gross <jgross at suse.com>
> Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
> ---
>  arch/x86/xen/spinlock.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> index 3d6e006..74756bb 100644
> --- a/arch/x86/xen/spinlock.c
> +++ b/arch/x86/xen/spinlock.c
> @@ -114,7 +114,6 @@ void xen_uninit_lock_cpu(int cpu)
>  	per_cpu(irq_name, cpu) = NULL;
>  }
>  
> -
>  /*
>   * Our init of PV spinlocks is split in two init functions due to us
>   * using paravirt patching and jump labels patching and having to do
> @@ -137,6 +136,8 @@ void __init xen_init_spinlocks(void)
>  	pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
>  	pv_lock_ops.wait = xen_qlock_wait;
>  	pv_lock_ops.kick = xen_qlock_kick;
> +
> +	pv_lock_ops.vcpu_is_preempted = xen_vcpu_stolen;
>  }
>  
>  /*
>

Peter Zijlstra

2016-Oct-21 05:40 UTC

head link

[PATCH v5 0/9] implement vcpu preempted check

On Thu, Oct 20, 2016 at 05:27:45PM -0400, Pan Xinhui wrote:
> 
> This patch set aims to fix lock holder preemption issues.
Thanks, this looks very good. I'll wait for ACKs from at least the KVM
people, since that was I think the most contentious patch.

David Laight

2016-Oct-21 11:27 UTC

head link

[PATCH v5 9/9] Documentation: virtual: kvm: Support vcpu preempted check

From: Pan Xinhui> Sent: 20 October 2016 22:28
> Commit ("x86, kvm: support vcpu preempted check") add one field
"__u8
> preempted" into struct kvm_steal_time. This field tells if one vcpu is
> running or not.
> 
> It is zero if 1) some old KVM deos not support this filed. 2) the vcpu is
> preempted. Other values means the vcpu has been preempted.
> 
> Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
> ---
>  Documentation/virtual/kvm/msr.txt | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virtual/kvm/msr.txt
b/Documentation/virtual/kvm/msr.txt
> index 2a71c8f..3376f13 100644
> --- a/Documentation/virtual/kvm/msr.txt
> +++ b/Documentation/virtual/kvm/msr.txt
> @@ -208,7 +208,8 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
>  		__u64 steal;
>  		__u32 version;
>  		__u32 flags;
> -		__u32 pad[12];
> +		__u8  preempted;
> +		__u32 pad[11];
>  	}
I think I'd be explicit about the 3 pad bytes you've left.

	David

xinhui

2016-Oct-24 08:08 UTC

head link

[PATCH v5 6/9] x86, kvm: support vcpu preempted check

This is new version for [PATCH v6 6/9] x86, kvm: support vcpu preempted check
change:
	an explicit pad[3] after __u8 preempted.

 From b876ea1a2a724c004b543b2c103a1f8faa5f106e Mon Sep 17 00:00:00 2001
From: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
Date: Thu, 20 Oct 2016 08:14:41 -0400
Subject: [PATCH v6 6/9] x86, kvm: support vcpu preempted check

Support the vcpu_is_preempted() functionality under KVM. This will
enhance lock performance on overcommitted hosts (more runnable vcpus
than physical cpus in the system) as doing busy waits for preempted
vcpus will hurt system performance far worse than early yielding.

Use one field of struct kvm_steal_time to indicate that if one vcpu
is running or not.

unix benchmark result:
host:  kernel 4.8.1, i5-4570, 4 cpus
guest: kernel 4.8.1, 8 vcpus

         test-case                       after-patch       before-patch
Execl Throughput                       |    18307.9 lps  |    11701.6 lps
File Copy 1024 bufsize 2000 maxblocks  |  1352407.3 KBps |   790418.9 KBps
File Copy 256 bufsize 500 maxblocks    |   367555.6 KBps |   222867.7 KBps
File Copy 4096 bufsize 8000 maxblocks  |  3675649.7 KBps |  1780614.4 KBps
Pipe Throughput                        | 11872208.7 lps  | 11855628.9 lps
Pipe-based Context Switching           |  1495126.5 lps  |  1490533.9 lps
Process Creation                       |    29881.2 lps  |    28572.8 lps
Shell Scripts (1 concurrent)           |    23224.3 lpm  |    22607.4 lpm
Shell Scripts (8 concurrent)           |     3531.4 lpm  |     3211.9 lpm
System Call Overhead                   | 10385653.0 lps  | 10419979.0 lps

Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
---
  arch/x86/include/uapi/asm/kvm_para.h |  4 +++-
  arch/x86/kernel/kvm.c                | 12 ++++++++++++
  arch/x86/kvm/x86.c                   | 18 ++++++++++++++++++
  3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h
b/arch/x86/include/uapi/asm/kvm_para.h
index 94dc8ca..1421a65 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -45,7 +45,9 @@ struct kvm_steal_time {
  	__u64 steal;
  	__u32 version;
  	__u32 flags;
-	__u32 pad[12];
+	__u8  preempted;
+	__u8  u8_pad[3];
+	__u32 pad[11];
  };
  
  #define KVM_STEAL_ALIGNMENT_BITS 5
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index edbbfc8..0b48dd2 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -415,6 +415,15 @@ void kvm_disable_steal_time(void)
  	wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
  }
  
+static bool kvm_vcpu_is_preempted(int cpu)
+{
+	struct kvm_steal_time *src;
+
+	src = &per_cpu(steal_time, cpu);
+
+	return !!src->preempted;
+}
+
  #ifdef CONFIG_SMP
  static void __init kvm_smp_prepare_boot_cpu(void)
  {
@@ -471,6 +480,9 @@ void __init kvm_guest_init(void)
  	if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
  		has_steal_clock = 1;
  		pv_time_ops.steal_clock = kvm_steal_clock;
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+		pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted;
+#endif
  	}
  
  	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c633de..a627537 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2057,6 +2057,8 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
  		&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
  		return;
  
+	vcpu->arch.st.steal.preempted = 0;
+
  	if (vcpu->arch.st.steal.version & 1)
  		vcpu->arch.st.steal.version += 1;  /* first time write, random junk */
  
@@ -2810,8 +2812,24 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
  	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
  }
  
+static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
+{
+	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
+		return;
+
+	if (unlikely(kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
+			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
+		return;
+
+	vcpu->arch.st.steal.preempted = 1;
+
+	kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
+			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
+}
+
  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
  {
+	kvm_steal_time_set_preempted(vcpu);
  	kvm_x86_ops->vcpu_put(vcpu);
  	kvm_put_guest_fpu(vcpu);
  	vcpu->arch.last_host_tsc = rdtsc();
-- 
2.4.11

xinhui

2016-Oct-24 08:12 UTC

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[PATCH v5 9/9] Documentation: virtual: kvm: Support vcpu preempted check

This is new version for [PATCH v6 9/9] Documentation: virtual: kvm: Support vcpu
preempted check
change:
	an explicit pad[3] after __u8 preempted.
	a typo fix in the commit log.
	
 From defac64d7c6a50d5f18ef64a7c776af3e21e8b68 Mon Sep 17 00:00:00 2001
From: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
Date: Thu, 20 Oct 2016 09:33:36 -0400
Subject: [PATCH v6 9/9] Documentation: virtual: kvm: Support vcpu preempted
check

Commit ("x86, kvm: support vcpu preempted check") add one field
"__u8
preempted" into struct kvm_steal_time. This field tells if one vcpu is
running or not.

It is zero if 1) some old KVM deos not support this filed. 2) the vcpu is
not preempted. Other values mean the vcpu has been preempted.

Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
Acked-by: Radim Kr?m?? <rkrcmar at redhat.com>
---
  Documentation/virtual/kvm/msr.txt | 9 ++++++++-
  1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/Documentation/virtual/kvm/msr.txt
b/Documentation/virtual/kvm/msr.txt
index 2a71c8f..ab2ab76 100644
--- a/Documentation/virtual/kvm/msr.txt
+++ b/Documentation/virtual/kvm/msr.txt
@@ -208,7 +208,9 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
  		__u64 steal;
  		__u32 version;
  		__u32 flags;
-		__u32 pad[12];
+		__u8  preempted;
+		__u8  u8_pad[3];
+		__u32 pad[11];
  	}
  
  	whose data will be filled in by the hypervisor periodically. Only one
@@ -232,6 +234,11 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
  		nanoseconds. Time during which the vcpu is idle, will not be
  		reported as steal time.
  
+		preempted: indicate the VCPU who owns this struct is running or
+		not. Non-zero values mean the VCPU has been preempted. Zero
+		means the VCPU is not preempted. NOTE, it is always zero if the
+		the hypervisor doesn't support this field.
+
  MSR_KVM_EOI_EN: 0x4b564d04
  	data: Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0
  	when disabled.  Bit 1 is reserved and must be zero.  When PV end of
-- 
2.4.11

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