linux-kernel - Re: [PATCH 1/1] psi: eliminate kthread_worker from psi trigger scheduling mechanism

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Message-ID: <20200604131215.GB4117@hirez.programming.kicks-ass.net>
Date:   Thu, 4 Jun 2020 15:12:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     mingo@...hat.com, hannes@...xchg.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        shakeelb@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/1] psi: eliminate kthread_worker from psi trigger
 scheduling mechanism

On Thu, May 28, 2020 at 12:54:42PM -0700, Suren Baghdasaryan wrote:
> Each psi group requires a dedicated kthread_delayed_work and
> kthread_worker. Since no other work can be performed using psi_group's
> kthread_worker, the same result can be obtained using a task_struct and
> a timer directly. This makes psi triggering simpler by removing lists
> and locks involved with kthread_worker usage and eliminates the need for
> poll_scheduled atomic use in the hot path.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
> This patch is meant to address Peter's request in [1] to pull
> kthread_queue_delayed_work() out from under rq->lock. This should also address
> the lockdep warning about possibility of a circular dependency described in [2]

I think you could've just fixed kthread_queue_delayed_work(), that code
is sub-optimal.

But I suppose this works too.