linux-kernel - Re: [tip: sched/core] sched/fair: Multi-LLC select_idle

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Date:   Wed, 14 Jun 2023 17:13:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     K Prateek Nayak <kprateek.nayak@....com>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Tejun Heo <tj@...nel.org>, x86@...nel.org,
        Gautham Shenoy <gautham.shenoy@....com>,
        Tim Chen <tim.c.chen@...el.com>
Subject: Re: [tip: sched/core] sched/fair: Multi-LLC select_idle_sibling()

On Wed, Jun 14, 2023 at 10:58:20PM +0800, Chen Yu wrote:
> On 2023-06-14 at 10:17:57 +0200, Peter Zijlstra wrote:
> > On Tue, Jun 13, 2023 at 04:00:39PM +0530, K Prateek Nayak wrote:
> > 
> > > >> - SIS_NODE_TOPOEXT - tip:sched/core + this patch
> > > >>                      + new sched domain (Multi-Multi-Core or MMC)
> > > >> 		     (https://lore.kernel.org/all/20230601153522.GB559993@hirez.programming.kicks-ass.net/)
> > > >> 		     MMC domain groups 2 nearby CCX.
> > > > 
> > > > OK, so you managed to get the NPS4 topology in NPS1 mode?
> > > 
> > > Yup! But it is a hack. I'll leave the patch at the end.
> > 
> > Chen Yu, could we do the reverse? Instead of building a bigger LLC
> > domain, can we split our LLC based on SNC (sub-numa-cluster) topologies?
> >
> Hi Peter,
> Do you mean with SNC enabled, if the LLC domain gets smaller? 
> According to the test, the answer seems to be yes.

No, I mean to build smaller LLC domains even with SNC disabled, as-if
SNC were active.