Commit 05ffc951 authored Nov 02, 2016 by Pan Xinhui Committed by Ingo Molnar Nov 22, 2016

locking/mutex: Break out of expensive busy-loop on...


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 <jgross@suse.com>
Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: benh@kernel.crashing.org
Cc: boqun.feng@gmail.com
Cc: bsingharora@gmail.com
Cc: dave@stgolabs.net
Cc: kernellwp@gmail.com
Cc: konrad.wilk@oracle.com
Cc: linuxppc-dev@lists.ozlabs.org
Cc: mpe@ellerman.id.au
Cc: paulmck@linux.vnet.ibm.com
Cc: paulus@samba.org
Cc: rkrcmar@redhat.com
Cc: virtualization@lists.linux-foundation.org
Cc: will.deacon@arm.com
Cc: xen-devel-request@lists.xenproject.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1478077718-37424-4-git-send-email-xinhui.pan@linux.vnet.ibm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 5aff60a1

kernel/locking/mutex.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -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();

		/*

kernel/locking/rwsem-xadd.c

+11 −3

Original line number	Diff line number	Diff line
		@@ -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;
		}