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

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Message-ID: <001601dc3d85$933dd540$b9b97fc0$@telus.net>
Date: Tue, 14 Oct 2025 20:41:20 -0700
From: "Doug Smythies" <dsmythies@...us.net>
To: "'Sergey Senozhatsky'" <senozhatsky@...omium.org>,
	"'Rafael J. Wysocki'" <rafael@...nel.org>
Cc: "'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>,
	"Doug Smythies" <dsmythies@...us.net>
Subject: RE: stable: commit "cpuidle: menu: Avoid discarding useful information" causes regressions

On 2025.10.14 18:30 Sergey Senozhatsky wrote:
> On (25/10/14 17:54), Rafael J. Wysocki wrote:
>> Sergey, can you please run the workload under turbostat on the base
>> 6.1.y and on 6.1.y with the problematic commit reverted and send the
>> turbostat output from both runs (note: turbostat needs to be run as
>> root)?
>
> Please find attached the turbostat logs for both cases.

The turbostat data suggests that power limit throttling is involved.
It also suggests, but I am not sure, that temperature limiting measures might be involved.

We need to know more about the test system involved here.
And we need to separate the variables.
What thermal limiting methods are being used? Is idle injection being used? Or CPU frequency limiting or both.
(I have very limited experience with thermald, and pretty much only use the TCC offset method.)
Power and Thermal throttling is never involved when I test idle governor changes.

If it were me, I would limit the maximum CPU frequency such that power limit throttling did not engage for the test. That would
likely also eliminate the need for any thermal limiting also.
The suggestion is to then repeat the test.

>From the discussion on this thread, it makes some sense that the selection of shallower idle states more often might have caused
more throttling leading to the apparent benchmark regression.

... Doug