Re: [PATCH] sched/fair: Prefer idle CPU to cache affinity

[Peter Zijlstra]

On Sat, Feb 27, 2021 at 02:56:07PM -0500, Rik van Riel wrote:
> On Fri, 2021-02-26 at 22:10 +0530, Srikar Dronamraju wrote:

> > +	if (sched_feat(WA_WAKER) && tnr_busy < tllc_size)
> > +		return this_cpu;
> 
> I wonder if we need to use a slightly lower threshold on
> very large LLCs, both to account for the fact that the
> select_idle_cpu code may not find the single idle CPU
> among a dozen busy ones, or because on a system with
> hyperthreading we may often be better off picking another
> LLC for HT contention issues?
> 
> Maybe we could use "tnr_busy * 4 <
> tllc_size * 3" or
> something like that?

How about:

	tnr_busy < tllc_size / topology_max_smt_threads()

?

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