linux-kernel - Re: [External] Re: [PATCH 2/3] sched/fair: Ignore isolated cpus in update_numa

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Message-ID: <1c7a042e-65e9-4774-a769-55b3c01af181@bytedance.com>
Date: Wed, 18 Dec 2024 15:19:43 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: K Prateek Nayak <kprateek.nayak@....com>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com
Cc: chengming.zhou@...ux.dev, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH 2/3] sched/fair: Ignore isolated cpus in
 update_numa_stat

Hello Prateek

在 2024/12/18 14:26, K Prateek Nayak 写道:
> Hello Chuyi,
> 
> On 12/16/2024 5:53 PM, Chuyi Zhou wrote:
>> [..snip..] @@ -2125,6 +2125,11 @@ static void update_numa_stats(struct 
>> task_numa_env *env,
>>       for_each_cpu(cpu, cpumask_of_node(nid)) {
> 
> Looking at sched_init_domains(), we only build sched domains only for
> active CPUs in housekeeping_cpumask(HK_TYPE_DOMAIN) so similar to the
> question on Patch 3, can we get away with just modifying this outer loop
> to:
> 
>      for_each_cpu_and(cpu, cpumask_of_node(nid), 
> housekeeping_cpumask(HK_TYPE_DOMAIN)) {
>          ...
>      }
> 
> Thoughts?
> 

We now have two ways of using isolated CPUs.

One is the isolcpus= kernel command line. 'isolcpus=0-7' would
exclude 0-7 cpus from housekeeping_cpumask without further restrictions 
on tasks' cpumasks. A typical case that could lead to errors is when a 
task's CPU mask covers all the CPUs in the system, causing the task to 
potentially be migrated to or woken up on CPUs 0-7. Commit 23d04d8 
resolves a similar issue in task wakeup.

The other is the isolated cpuset partition:
  mkdir blue
  echo 5-8 > blue/cpuset.cpus
  echo "isolated" > blue/cpuset.cpus.partition

The 5-8 cpus now is also a isolated domain, but 5-8 would not be 
excluded from housekeeping_cpumask. The tasks' cpumask in blue cgroup 
would be restricted to 5-8.

I thinks in update_numa_stats(), only using 
housekeeping_cpumask(HK_TYPE_DOMAIN) is not enough because it cannot 
skip those isolated cpuset partitions.

Thanks.