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

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Message-ID: <1295986386.28776.1101.camel@laptop>
Date:	Tue, 25 Jan 2011 21:13:06 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com, Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH 16/16] KVM-GST: adjust scheduler cpu power

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.


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