linux-kernel - Re: [PATCH v2 0/2] sched/topology: optimize topology_span

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Message-ID: <97643a07-bc9d-41d5-8e3c-e251f510129b@wanadoo.fr>
Date: Thu, 29 Aug 2024 08:11:41 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org
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 v2 0/2] sched/topology: optimize topology_span_sane()

Le 28/08/2024 à 16:09, Yury Norov a écrit :
> Ping again?
> 

Hi,

The covert letter is v2, but the patch below it are without v2.

In patch 1/2, the Suggested-by: tags in v1 have been removed in this new 
version :(.

CJ

> On Wed, Aug 14, 2024 at 09:35:04AM -0700, Yury Norov wrote:
>> Ping?
>>
>> On Wed, Aug 07, 2024 at 12:05:19PM -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:
>>>   - defer initialization of 'mc' in patch #1 @Chen Yu;
>>>   - more comments from Valentin Schneider.
>>>
>>>
>>> Yury Norov (2):
>>>    sched/topology: pre-compute topology_span_sane() loop params
>>>    sched/topology: optimize topology_span_sane()
>>>
>>>   kernel/sched/topology.c | 20 ++++++++++++++++++--
>>>   1 file changed, 18 insertions(+), 2 deletions(-)
>>>
>>> -- 
>>> 2.43.0
> 
>