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

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Date:	Fri, 25 Mar 2011 22:06:23 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Venkatesh Pallipadi <venki@...gle.com>
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 Fri, 2011-03-18 at 18:23 -0700, Venkatesh Pallipadi wrote:
> >        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.

D'0h yeah, I missed the conditional execution of wake_affine there, silly me.

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