linux-kernel - Re: [RFC][PATCH 09/14] sched: Dynamically allocate sched_domain/sched

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Message-ID: <AANLkTikUGwkOwUoGcti0SOFWVKxAMZNUk9c30oBRFmMx@mail.gmail.com>
Date:	Fri, 18 Mar 2011 18:23:58 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Anton Blanchard <anton@....ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Paul Turner <pjt@...gle.com>, Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Andreas Herrmann <andreas.herrmann3@....com>
Subject: Re: [RFC][PATCH 09/14] sched: Dynamically allocate
 sched_domain/sched_group data-structures

On Mon, Mar 14, 2011 at 8:06 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> @@ -1721,10 +1724,11 @@ select_task_rq_fair(struct rq *rq, struc
>        }
>
>        if (affine_sd) {
> -               if (cpu == prev_cpu || wake_affine(affine_sd, p, sync))
> -                       return select_idle_sibling(p, cpu);
> -               else
> -                       return select_idle_sibling(p, prev_cpu);
> +               if (wake_affine(affine_sd, p, sync))
> +                       prev_cpu = cpu;
> +
> +               new_cpu = select_idle_sibling(p, prev_cpu);
> +               goto unlock;
>        }
>
>        while (sd) {

This would result in going through wake_affine() doing all
effective_load stuff even with cpu == prev_cpu. No?
So, we need either if (cpu != prev_cpu && wake_affine(affine_sd, p,
sync)) or an check at the start to have want_affine=0 for this case.

Overall patchset looks great!

Thanks,
Venki
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