linux-kernel - Re: stable: commit "cpuidle: menu: Avoid discarding useful information" causes regressions

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Message-ID: <CAJZ5v0gqKcmXEObq6UmfTBXgueHw3eMk+CM74-FLjB3wk3WjGQ@mail.gmail.com>
Date: Thu, 16 Oct 2025 11:47:10 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Christian Loehle <christian.loehle@....com>, 
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>, Sasha Levin <sashal@...nel.org>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Tomasz Figa <tfiga@...omium.org>, stable@...r.kernel.org
Subject: Re: stable: commit "cpuidle: menu: Avoid discarding useful
 information" causes regressions

On Thu, Oct 16, 2025 at 6:54 AM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (25/10/15 15:08), Rafael J. Wysocki wrote:
> > On Wed, Oct 15, 2025 at 3:56 AM Sergey Senozhatsky
> > <senozhatsky@...omium.org> wrote:
> > >
> > > On (25/10/14 16:02), Rafael J. Wysocki wrote:
> > > > > >> Would it be possible to check if the mainline has this issue?  That
> > > > > >> is, compare the benchmark results on unmodified 6.17 (say) and on 6.17
> > > > > >> with commit 85975daeaa4 reverted?
> > > > > >
> > > > > > I don't think mainline kernel can run on those devices (due to
> > > > > > a bunch of downstream patches).  Best bet is 6.12, I guess.
> > > > >
> > > > > Depending on what Rafael is expecting here you might just get
> > > > > away with copying menu.c from mainline, the interactions to other
> > > > > subsystems are limited fortunately.
> > > >
> > > > Yeah, that'd be sufficiently close.
> > >
> > > Test results for menu.c from linux-next are within regressed range: 78.5
> >
> > So please check if the attached patch makes any difference.
>
> From what I can tell the patch fixes it!

Well, that's something.

As far as I'm concerned, this change can be made.

>From a purely theoretical standpoint, arguments can be made for doing
it as well as for the current code and none of them is definitely
preferable.

The current approach was chosen because it led to lower latency which
should result in better performance, but after the patch the code is
closer to what was done before.

Let me submit it officially and we'll see what people will have to say.