Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenariosin PLE handler

[Raghavendra K T]

On 10/03/2012 10:55 PM, Avi Kivity wrote:
> On 10/03/2012 04:29 PM, Raghavendra K T wrote:
> > * Avi Kivity <avi@xxxxxxxxxx> [2012-09-27 14:03:59]:
> >
> > > On 09/27/2012 01:23 PM, Raghavendra K T wrote:
> > > > >
> > [...]
> > > > 2) looking at the result (comparing A & C) , I do feel we have
> > > > significant in iterating over vcpus (when compared to even vmexit)
> > > > so We still would need undercommit fix sugested by PeterZ (improving by
> > > > 140%). ?
> > >
> > > Looking only at the current runqueue?  My worry is that it misses a lot
> > > of cases.  Maybe try the current runqueue first and then others.
> >
> > Okay. Do you mean we can have something like
> >
> > +       if (rq->nr_running == 1 && p_rq->nr_running == 1) {
> > +               yielded = -ESRCH;
> > +               goto out_irq;
> > +       }
> >
> > in the Peter's patch ?
> >
> > ( I thought lot about && or || . Both seem to have their own cons ).
> > But that should be only when we have short term imbalance, as PeterZ
> > told.
>
> I'm missing the context.  What is p_rq?

p_rq is the run queue of target vcpu.
What I was trying below was to address Rik concern. Suppose
rq of source vcpu has one task, but target probably has two task,
with a eligible vcpu waiting to be scheduled.

> What I mean was:
>
>    if can_yield_to_process_in_current_rq
>       do that
>    else if can_yield_to_process_in_other_rq
>       do that
>    else
>       return -ESRCH

I think you are saying we have to check the run queue of the
source vcpu, if we have a vcpu belonging to same VM and try yield to 
that? ignoring whatever the target vcpu we received for yield_to.

Or is it that kvm_vcpu_yield_to should now check the vcpus of same vm
belonging to same run queue first. If we don't succeed, go again for
a vcpu in different runqueue.
Does it add more overhead especially in <= 1x scenario?

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