Re: [PATCH 16/16] KVM-GST: adjust scheduler cpu power

[Glauber Costa]

On Tue, 2011-01-25 at 22:07 +0100, Peter Zijlstra wrote:
> On Tue, 2011-01-25 at 18:47 -0200, Glauber Costa wrote:
> > On Tue, 2011-01-25 at 21:13 +0100, Peter Zijlstra wrote:
> > > On Tue, 2011-01-25 at 18:02 -0200, Glauber Costa wrote:
> > > 
> > > > I fail to see how does clock_task influence cpu power.
> > > > If we also have to touch clock_task for better accounting of other
> > > > stuff, it is a separate story.
> > > > But for cpu_power, I really fail. Please enlighten me.
> > > 
> > > static void update_rq_clock_task(struct rq *rq, s64 delta)
> > > {
> > >         s64 irq_delta;
> > > 
> > >         irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;
> > > 
> > >         if (irq_delta > delta)
> > >                 irq_delta = delta;
> > > 
> > >         rq->prev_irq_time += irq_delta;
> > >         delta -= irq_delta;
> > >         rq->clock_task += delta;
> > > 
> > >         if (irq_delta && sched_feat(NONIRQ_POWER))
> > >                 sched_rt_avg_update(rq, irq_delta);
> > > }
> > > 
> > > its done through that sched_rt_avg_update() (should probably rename
> > > that), it computes a floating average of time not spend on fair tasks.
> > > 
> > It creates a dependency on CONFIG_IRQ_TIME_ACCOUNTING, though.
> > This piece of code is simply compiled out if this option is disabled.
> 
> We can pull this bit out and make the common bit also available for
> paravirt.

scale_rt_power() seems to do the right thing, but all the path leading
to it seem to work on rq->clock, rather than rq->clock_task.

Although I do can experiment with that as well, could you please
elaborate on what are your reasons to prefer this over than variations
of the method I proposed?




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