linux-kernel - Re: [PATCH 1/2] sched/isolation: Merge individual nohz_full features into a common housekeeping flag

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Message-ID: <20230207125900.GA24523@blackbody.suse.cz>
Date:   Tue, 7 Feb 2023 13:59:00 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Waiman Long <longman@...hat.com>,
        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 1/2] sched/isolation: Merge individual nohz_full features
 into a common housekeeping flag

On Tue, Feb 07, 2023 at 12:49:41PM +0100, Frederic Weisbecker <frederic@...nel.org> wrote:
> But what do we need these annotations for? The only outcome I've ever
> seen with these is that it confuses everyone.

Take that as a note of a lone actor then who found it useful documenting
relations between various parts of the code.

> This way I can add the support for each part smoothly.

Yeah, that makes sense.

> For example first patch moves HK_TYPE_TIMER to HK_TYPE_KERNEL_NOISE
> and unbound timers are supported by cpuset.kernel_noise, second patch
> moves HK_TYPE_WQ to HK_TYPE_KERNEL_NOISE and unbound workqueues are
> supported by cpuset.kernel_noise, etc until all of them turned by
> nohz_full= are supported...

So does this mean you'll re-introduce the finer grained HK_* flags
again?

The idea (not only mine?) is that this would extend
cpuset.cpus.partition that only allows HK_TYPE_DOMAIN analogy. The
mapping to individual flags may not be exposed to users. The graduality
could be achieved by adding more flags under user_exposed_term.

Just to be on the same page -- that's how I understand it, the original
HK_* resolution turned out impractical for users and that's why the
direction is towards some loose combinations representing user
intentions. Is that right?

Cheers,
Michal

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