linux-kernel - Re: [PATCH v3 0/3] sched/topology: optimize topology_span

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Message-ID: <Zvr4s9ErpD9F81YH@yury-ThinkPad>
Date: Mon, 30 Sep 2024 12:14:59 -0700
From: Yury Norov <yury.norov@...il.com>
To: linux-kernel@...r.kernel.org,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Chen Yu <yu.c.chen@...el.com>, Leonardo Bras <leobras@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH v3 0/3] sched/topology: optimize topology_span_sane()

Ping again?

On Sat, Sep 14, 2024 at 09:54:43AM -0700, Yury Norov wrote:
> Ping?
> 
> On Mon, Sep 02, 2024 at 11:36:04AM -0700, Yury Norov wrote:
> > The function may call cpumask_equal with tl->mask(cpu) == tl->mask(i),
> > even when cpu != i. In such case, cpumask_equal() would always return
> > true, and we can proceed to the next iteration immediately.
> > 
> > Valentin Schneider shares on it:
> > 
> >   PKG can potentially hit that condition, and so can any
> >   sched_domain_mask_f that relies on the node masks...
> > 
> >   I'm thinking ideally we should have checks in place to
> >   ensure all node_to_cpumask_map[] masks are disjoint,
> >   then we could entirely skip the levels that use these
> >   masks in topology_span_sane(), but there's unfortunately
> >   no nice way to flag them... Also there would be cases
> >   where there's no real difference between PKG and NODE
> >   other than NODE is still based on a per-cpu cpumask and
> >   PKG isn't, so I don't see a nicer way to go about this.
> > 
> > v1: https://lore.kernel.org/lkml/ZrJk00cmVaUIAr4G@yury-ThinkPad/T/
> > v2: https://lkml.org/lkml/2024/8/7/1299
> > v3:
> >  - add topology_cpumask_equal() helper in #3;
> >  - re-use 'cpu' as an iterator int the for_each_cpu() loop;
> >  - add proper versioning for all patches.
> > 
> > Yury Norov (3):
> >   sched/topology: pre-compute topology_span_sane() loop params
> >   sched/topology: optimize topology_span_sane()
> >   sched/topology: reorganize topology_span_sane() checking order
> > 
> >  kernel/sched/topology.c | 29 +++++++++++++++++++++++++----
> >  1 file changed, 25 insertions(+), 4 deletions(-)
> > 
> > -- 
> > 2.43.0