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

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Message-ID: <20251205104941.GR2528459@noisy.programming.kicks-ass.net>
Date: Fri, 5 Dec 2025 11:49:41 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Don <joshdon@...gle.com>
Cc: Blake Jones <blakejones@...gle.com>, 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

On Thu, Dec 04, 2025 at 02:56:47PM -0800, Josh Don wrote:
> 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?

I've stuck it on the pile for post -rc1 time.