Subject: Re: [PATCH v2 0/4] implement vcpu preempted check

From: Peter Zijlstra <[email-masked]>
Date: Wed, 6 Jul 2016 08:52:55 +0200

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?

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