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Subject: Re: [PATCH 16/16] KVM-GST: adjust scheduler cpu power
From: Glauber Costa <glommer@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, aliguori@us.ibm.com,
        Rik van Riel <riel@redhat.com>,
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Organization: Red Hat
Date: Tue, 25 Jan 2011 18:47:35 -0200
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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.