linux-kernel - Re: [PATCH 2/2] sched/isolation: Add cpu_is

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Message-ID: <20230206154710.GC21332@blackbody.suse.cz>
Date:   Mon, 6 Feb 2023 16:47:10 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Hocko <mhocko@...e.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Leonardo <leobras@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, cgroups@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/2] sched/isolation: Add cpu_is_isolated() API

Hello.

On Fri, Feb 03, 2023 at 10:53:46PM -0500, Waiman Long <longman@...hat.com> wrote:
> CPUs in an isolated cpuset partition is similar to HK_TYPE_DOMAIN CPUs as
> load balancing is disabled. I can add an API to access the cpumask and add
> to this API. However, that list is dynamic as it can be changed at run time.
> Will that be a problem?

I can see a problem already -- as a CPU can be dynamically switched to
"isolated" mode so should all dependent operations support that (switch)
too, i.e. the CPUs local PCP caches would have to be drained when the
CPU enters isolation.

> Or should that be used separately?

It'd be nice to have both (cpuset and cmdline flags) eventually unified.

Alas, it only leads me conservatively to:

#ifndef CONFIG_CPUSETS
// the proposed implementaion
else
static inline bool cpu_is_isolated(int cpu) {
	return true;
}
#endif

My 0.02€,
Michal


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