Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

From: Peter Zijlstra
Date: Fri Feb 22 2013 - 04:39:44 EST

On Fri, 2013-02-22 at 17:10 +0800, Michael Wang wrote:
> On 02/22/2013 04:21 PM, Peter Zijlstra wrote:
> > On Fri, 2013-02-22 at 10:36 +0800, Michael Wang wrote:
> >> According to my understanding, in the old world, wake_affine() will
> >> only
> >> be used if curr_cpu and prev_cpu share cache, which means they are in
> >> one package, whatever search in llc sd of curr_cpu or prev_cpu, we
> >> won't
> >> have the chance to spread the task out of that package.
> >
> > Nah, look at where SD_WAKE_AFFINE is set. Only 'remote/big' NUMA domains
> > don't have it set, but 'small' NUMA systems will have it set over the
> > entire domain tree.
> Oh, I missed that point...
> But I don't get the reason to make NUMA level affine, cpus in different
> nodes share cache? doesn't make sense...

Contrary, it makes more sense, the more expensive it is to run 'remote'
the better it is to pull 'related' tasks together.

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