linux-kernel - Re: [PATCH v5] sched: reorder some fields in struct rq

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Message-ID: <CABk29NskTSV1JUT=_08sQXaWkpHyHb5RKYLVeTSHdx+QMiw5dA@mail.gmail.com>
Date: Thu, 4 Dec 2025 14:56:47 -0800
From: Josh Don <joshdon@...gle.com>
To: Blake Jones <blakejones@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Madadi Vineeth Reddy <vineethr@...ux.ibm.com>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] sched: reorder some fields in struct rq

Hi Blake,

On Mon, Dec 1, 2025 at 6:37 PM Blake Jones <blakejones@...gle.com> wrote:
>
> This colocates some hot fields in "struct rq" to be on the same cache line
> as others that are often accessed at the same time or in similar ways.
[snip]
> Signed-off-by: Blake Jones <blakejones@...gle.com>
> Reviewed-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
> Tested-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>

Sorry, I thought I had already included a review tag when I responded
to the earlier version of this.

Reviewed-by: Josh Don <joshdon@...gle.com>

> ---
>  kernel/sched/sched.h | 80 +++++++++++++++++++++++++++-----------------
>  1 file changed, 50 insertions(+), 30 deletions(-)
>
> v4 -> v5 changes:
> - Resynced with sched/core.
>   Link to v4: https://lore.kernel.org/lkml/20251029185458.3040228-1-blakejones@google.com/T/#u
>
> v3 -> v4 changes:
> - Updated based on review comments from peterz@...radead.org:
>   updated block comment in struct rq, moved "nr_iowait" to the end of the
>   structure, and added "__no_randomize_layout" tag to the structure.
>   Link to v3: https://lore.kernel.org/lkml/20251028080348.2177469-1-blakejones@google.com/T/#u
>
> v2 -> v3 changes:
> - Resynced and retested. Results are consistent with v2.
>   Link to v2: https://lore.kernel.org/lkml/20250730205644.2595052-1-blakejones@google.com/T/#u
>
> v1 -> v2 changes:
> - Resynced to tip/sched/core tree, which has removed CONFIG_SMP.
>   Link to v1: https://lore.kernel.org/lkml/20250722201339.1198239-1-blakejones@google.com/T/#u
>
> v1 was sent on July 22 of this year, over four months ago.

The patch is straightforward and the results look compelling;
Peter/Ingo, any thoughts?

Best,
Josh