linux-kernel - Re: [PATCH] sched/idle: disable tick in idle=poll idle entry

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Message-ID: <20230608083400.GH998233@hirez.programming.kicks-ass.net>
Date:   Thu, 8 Jun 2023 10:34:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/idle: disable tick in idle=poll idle entry

On Wed, Jun 07, 2023 at 10:10:46PM -0300, Marcelo Tosatti wrote:
> 
> Commit a5183862e76fdc25f36b39c2489b816a5c66e2e5 
> ("tick/nohz: Conditionally restart tick on idle exit") allows
> a nohz_full CPU to enter idle and return from it with the 
> scheduler tick disabled (since the tick might be undesired noise).
> 
> The idle=poll case still unconditionally restarts the tick when entering
> idle.
> 
> To reduce the noise for that case as well, stop the tick when entering
> idle, for the idle=poll case.
> 
> tick_nohz_idle_exit (called if the NEED_RESCHED bit is set) 
> is responsible for re-enabling the tick when necessary. 

Who cares and why?