linux-kernel - Re: [PATCH 4/6] tick/nohz: Move nohz_full related fields out of hot task struct's places

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Message-ID: <xhsmh4ivag4md.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Thu, 17 Jul 2025 18:32:26 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>, LKML
 <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>, Andrew Morton
 <akpm@...ux-foundation.org>, Ingo Molnar <mingo@...hat.com>, Marcelo
 Tosatti <mtosatti@...hat.com>, Michal Hocko <mhocko@...nel.org>, Oleg
 Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas
 Gleixner <tglx@...utronix.de>, Vlastimil Babka <vbabka@...e.cz>,
 linux-mm@...ck.org
Subject: Re: [PATCH 4/6] tick/nohz: Move nohz_full related fields out of hot
 task struct's places

On 03/07/25 16:07, Frederic Weisbecker wrote:
> nohz_full is a feature that only fits into rare and very corner cases.
> Yet distros enable it by default and therefore the related fields are
> always reserved in the task struct.
>
> Those task fields are stored in the middle of cacheline hot places such
> as cputime accounting and context switch counting, which doesn't make
> any sense for a feature that is disabled most of the time.
>
> Move the nohz_full storage to colder places.
>
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>

task_struct is still a bloody maze to me, but AFAICT there's *at least one*
full non-optional cacheline - the signal handling faff - between cputime
accounting and this new location, so:

Reviewed-by: Valentin Schneider <vschneid@...hat.com>