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

[Waiman Long]

On 07/06/2016 02:52 AM, 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?
>
> Waiman, could you see if you can utilize this to get rid of the
> SPIN_THRESHOLD in qspinlock_paravirt?

That API is certainly useful to make the paravirt spinlock perform 
better. However, I am not sure if we can completely get rid of the 
SPIN_THRESHOLD at this point. It is not just the kvm, the xen code need 
to be modified as well.

Cheers,
Longman