linux-kernel - Re: [PATCH 6/7] KVM-GST: adjust scheduler cpu power

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Date:	Tue, 14 Jun 2011 12:42:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Avi Kivity <avi@...hat.com>,
	Anthony Liguori <aliguori@...ibm.com>,
	Eric B Munson <emunson@...bm.net>
Subject: Re: [PATCH 6/7] KVM-GST: adjust scheduler cpu power

On Mon, 2011-06-13 at 19:31 -0400, Glauber Costa wrote:
> @@ -1981,12 +1987,29 @@ static void update_rq_clock_task(struct rq
> *rq, s64 delta)
>  
>         rq->prev_irq_time += irq_delta;
>         delta -= irq_delta;
> +#endif
> +#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
> +       if (static_branch((&paravirt_steal_rq_enabled))) {

Why is that a different variable from the touch_steal_time() one?

> +
> +               steal = paravirt_steal_clock(cpu_of(rq));
> +               steal -= rq->prev_steal_time_acc;
> +
> +               rq->prev_steal_time_acc += steal;

You have this addition in the wrong place, when you clip:

> +               if (steal > delta)
> +                       steal = delta;

you just lost your steal delta, so the addition to prev_steal_time_acc
needs to be after the clip.

> +               delta -= steal;
> +       }
> +#endif
> +
>         rq->clock_task += delta;
>  
> -       if (irq_delta && sched_feat(NONIRQ_POWER))
> -               sched_rt_avg_update(rq, irq_delta);
> +       if ((irq_delta + steal) && sched_feat(NONTASK_POWER))
> +               sched_rt_avg_update(rq, irq_delta + steal);
>  } 
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