Commit-ID: 05ffc951392df57edecc2519327b169210c3df75
Gitweb: http://git.kernel.org/tip/05ffc951392df57edecc2519327b169210c3df75
Author: Pan Xinhui <xinhui....@linux.vnet.ibm.com>
AuthorDate: Wed, 2 Nov 2016 05:08:30 -0400
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Tue, 22 Nov 2016 12:48:10 +0100
locking/mutex: Break out of expensive busy-loop on
{mutex,rwsem}_spin_on_owner() when owner vCPU is preempted
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.
Break out of the loop if the vCPU is preempted: if vcpu_is_preempted(cpu)
is true.
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
Tested-by: Juergen Gross <jgr...@suse.com>
Signed-off-by: Pan Xinhui <xinhui....@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Acked-by: Christian Borntraeger <borntrae...@de.ibm.com>
Acked-by: Paolo Bonzini <pbonz...@redhat.com>
Cc: david.lai...@aculab.com
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: b...@kernel.crashing.org
Cc: boqun.f...@gmail.com
Cc: bsinghar...@gmail.com
Cc: d...@stgolabs.net
Cc: kernel...@gmail.com
Cc: konrad.w...@oracle.com
Cc: linuxppc-...@lists.ozlabs.org
Cc: m...@ellerman.id.au
Cc: paul...@linux.vnet.ibm.com
Cc: pau...@samba.org
Cc: rkrc...@redhat.com
Cc: virtualizat...@lists.linux-foundation.org
Cc: will.dea...@arm.com
Cc: xen-devel-requ...@lists.xenproject.org
Cc: xen-de...@lists.xenproject.org
Link:
http://lkml.kernel.org/r/1478077718-37424-4-git-send-email-xinhui....@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
kernel/locking/mutex.c | 13 +++++++++++--
kernel/locking/rwsem-xadd.c | 14 +++++++++++---
2 files changed, 22 insertions(+), 5 deletions(-)
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index c073168..9b34961 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -364,7 +364,11 @@ bool mutex_spin_on_owner(struct mutex *lock, struct
task_struct *owner)
*/
barrier();
- if (!owner->on_cpu || need_resched()) {
+ /*
+ * Use vcpu_is_preempted to detect lock holder preemption issue.
+ */
+ if (!owner->on_cpu || need_resched() ||
+ vcpu_is_preempted(task_cpu(owner))) {
ret = false;
break;
}
@@ -389,8 +393,13 @@ static inline int mutex_can_spin_on_owner(struct mutex
*lock)
rcu_read_lock();
owner = __mutex_owner(lock);
+
+ /*
+ * 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();
/*
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 263e744..6315060 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 +366,12 @@ 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.
+ */
+ if (!owner->on_cpu || need_resched() ||
+ vcpu_is_preempted(task_cpu(owner))) {
rcu_read_unlock();
return false;
}
