linux-kernel - Re: [PATCH v2 0/4] implement vcpu preempted check

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Date:	Wed, 6 Jul 2016 12:44:58 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Cc:	linux-s390@...r.kernel.org, dave@...olabs.net, mpe@...erman.id.au,
	boqun.feng@...il.com, will.deacon@....com,
	linux-kernel@...r.kernel.org, waiman.long@....com,
	virtualization@...ts.linux-foundation.org, mingo@...hat.com,
	paulus@...ba.org, benh@...nel.crashing.org, schwidefsky@...ibm.com,
	paulmck@...ux.vnet.ibm.com, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 0/4] implement vcpu preempted check



On 06/07/2016 08:52, Peter Zijlstra wrote:
> On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote:
>> change fomr 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
>>
> 
> Paolo, could you help out with an (x86) KVM interface for this?

If it's just for spin loops, you can check if the version field in the
steal time structure has changed.

Paolo

> Waiman, could you see if you can utilize this to get rid of the
> SPIN_THRESHOLD in qspinlock_paravirt?
>