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[66.183.142.209]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8241d1cc84asm3772957b3a.23.2026.02.04.16.45.16 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 04 Feb 2026 16:45:16 -0800 (PST) From: "Doug Smythies" To: "'Rafael J. Wysocki'" , "'Christian Loehle'" , "'Harshvardhan Jha'" , "'Sergey Senozhatsky'" Cc: "'Sasha Levin'" , "'Greg Kroah-Hartman'" , , , "'Daniel Lezcano'" , "Doug Smythies" References: <39c7d882-6711-4178-bce6-c1e4fc909b84@arm.com> <005401dc64a4$75f1d770$61d58650$@telus.net> <6347bf83-545b-4e85-a5af-1d0c7ea24844@arm.com> <849ee0ff-e15b-4b69-84de-6503e3b3168d@oracle.com> <003e01dc9013$e3bc5060$ab34f120$@telus.net> <004e01dc90b1$4b28f9e0$e17aeda0$@telus.net> <002601dc916e$6acbe650$4063b2f0$@telus.net> <3b0720d2-9b72-48d0-998a-1fd091cec44f@arm.com> <5d4b624c-f993-49aa-95ab-5f279f7f6599@oracle.com> <8fd5a9d4-e555-4db1-aa02-8fe5b8a2962c@arm.com> <3395ad0b-425e-40f5-844c-627cff471353@oracle.com> <3f0cfac2-b753-413c-9a7e-0892c23cdbf4@arm.com> In-Reply-To: Subject: RE: Performance regressions introduced via Revert "cpuidle: menu: Avoid discarding useful information" on 5.15 LTS Date: Wed, 4 Feb 2026 16:45:18 -0800 Message-ID: <005401dc9638$b3e2ea40$1ba8bec0$@telus.net> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Content-Language: en-ca Thread-Index: AQHo/NwLGJZTeO77XmxNlnPhSwOGkAKJCFtJAex1orYBu9KCwgGuBEkcAe/o8FIB5x3ejgFHdCyGAj6zVaYCBiXTGgCgaPhQAgSxF3QCdRKf4wD6zBBnAsuKJa4A5XOx7rSCKx/Q On 2026.02.03 08:46 Rafael J. Wysocki wrote: -----Original Message----- From: Rafael J. Wysocki =20 Sent: February 3, 2026 8:46 AM To: Christian Loehle Cc: Harshvardhan Jha ; Rafael J. Wysocki = ; Doug Smythies ; Sasha Levin = ; Greg Kroah-Hartman ; = linux-pm@vger.kernel.org; stable@vger.kernel.org; Daniel Lezcano = ; Sergey Senozhatsky = Subject: Re: Performance regressions introduced via Revert "cpuidle: = menu: Avoid discarding useful information" on 5.15 LTS > On Tue, Feb 3, 2026 at 10:31=E2=80=AFAM Christian Loehle wrote: >> On 2/3/26 09:16, Harshvardhan Jha wrote: >>> On 03/02/26 2:37 PM, Christian Loehle wrote: >>>> On 2/2/26 17:31, Harshvardhan Jha wrote: > > [cut] > >>>> FWIW Jasper Lake seems to be supported from 5.6 on, see >>>> b2d32af0bff4 ("x86/cpu: Add Jasper Lake to Intel family") >>> >>> Oh I see, but shouldn't avoiding regressions on established = platforms be >>> a priority over further optimizing for specific newer platforms like >>> Jasper Lake? >>> >> Well avoiding regressions on established platforms is what lead to >> 10fad4012234 Revert "cpuidle: menu: Avoid discarding useful = information" >> being applied and backported. >> The expectation for stable is that we avoid regressions and = potentially >> miss out on improvements. If you want the latest greatest performance = you >> should probably run a latest greatest kernel. >> The original >> 85975daeaa4d cpuidle: menu: Avoid discarding useful information >> was seen as a fix and overall improvement, > > Note, however, that commit 85975daeaa4d carries no Fixes: tag and no > Cc: stable. It was picked up into stable kernels for another reason. > >> that's why it was backported, but Sergey's regression report = contradicted that. > > Exactly. > >> What is "established" and "newer" for a stable kernel is quite = handwavy >> IMO but even here Sergey's regression report is a clear data point... > > Which wasn't known at the time commit 85975daeaa4d went in. > >> Your report is only restoring 5.15 (and others) performance to 5.15 >> upstream-ish levels which is within the expectations of running a = stable >> kernel. No doubt it's frustrating either way! > > That is a consequence of the time it takes for mainline changes to > propagate to distributions (Chrome OS in this particular case) at > which point they get tested on a wider range of systems. Until that > happens, it is not really guaranteed that the given change will stay > in. > > In this particular case, restoring commit 85975daeaa4d would cause the > same problems on the systems adversely affected by it to become > visible again and I don't think it would be fair to say "Too bad" to > the users of those systems. IMV, it cannot be restored without a way > to at least limit the adverse effect on performance. I have been going over the old emails and the turbostat data again and = again and again. I still do not understand how to breakdown Sergey's results into its component contributions. I am certain there is power limit throttling during the test, but have no idea to much or how little it contributes = to the differing results. I think more work is needed to fully understand Sergey's test results = from October. I struggle with the dramatic test results difference of base=3D84.5 and = revert=3D59.5 as being due to only the idle code changes. That is why I keep asking for a test to be done with the CPU clock = frequency limited such that power limit throttling can not occur. I don't know what limit = to use, but suggest 2.2 GHZ to start with. Capture turbostat data with the tests. And record = the test results. @Sergey: are you willing to do the test? > > I have an idea to test, but getting something workable out of it may > be a challenge, even if it turns out to be a good one.