Re: [PATCH RFC 2/2] kvm: Be courteous to other VMs in overcommittedscenario in PLE handler

[Raghavendra K T]

On 09/21/2012 07:22 PM, Rik van Riel wrote:
> On 09/21/2012 09:46 AM, Takuya Yoshikawa wrote:
> > On Fri, 21 Sep 2012 17:30:20 +0530
> > Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > > From: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> > >
> > > When PLE handler fails to find a better candidate to yield_to, it
> > > goes back and does spin again. This is acceptable when we do not
> > > have overcommit.
> > > But in overcommitted scenarios (especially when we have large
> > > number of small guests), it is better to yield.
> > >
> > > Reviewed-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> > > ---
> > > virt/kvm/kvm_main.c | 4 ++++
> > > 1 files changed, 4 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index 8323685..713b677 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -1660,6 +1660,10 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
> > > }
> > > }
> > > }
> > > + /* In overcommitted cases, yield instead of spinning */
> > > + if (!yielded && rq_nr_running() > 1)
> > > + schedule();
> >
> > How about doing cond_resched() instead?
>
> Actually, an actual call to yield() may be better.
>
> That will set scheduler hints to make the scheduler pick
> another task for one round, while preserving this task's
> top position in the runqueue.

I am not a scheduler expert, but I am also inclined towards
Rik's suggestion here since we set skip buddy here. Takuya?

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