linux-kernel - Re: [PATCH v2] sched/idle: disable tick in idle=poll idle entry

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Message-ID: <aQJWjteaSaaC1dnU@tpad>
Date: Wed, 29 Oct 2025 15:01:50 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/idle: disable tick in idle=poll idle entry

On Wed, Oct 29, 2025 at 03:00:56PM -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.
> 
> Change tick_nohz_full_kick_cpu to set NEED_RESCHED bit, to handle the
> case where a new timer is added from an interrupt. This breaks out of
> cpu_idle_poll and rearms the timer if necessary.

Frederic,

As a reminder, this is the original patch and discussion:

https://patchew.org/linux/ZIEqlkIASx2F2DRF@tpad/