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

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Peter Zijlstra <peterz@infradead.org> [2021-03-01 16:44:42]:

> 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()
> 
> ?

Isn't topology_max_smt_threads only for x86 as of today?
Or Am I missing out?


-- 
Thanks and Regards
Srikar Dronamraju