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Tue, 11 Aug 2026 10:25:37 -0700 (PDT) Received: from [10.245.245.29] ([134.191.227.48]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4814a72ce1esm6565288f8f.34.2026.08.11.10.25.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Aug 2026 10:25:36 -0700 (PDT) Message-ID: <8cdc18896a03d13ebea065ab27991a71e460069b.camel@gmail.com> Subject: Re: [PATCH] intel_idle: Fix C6S and C10 latency values for Pantherlake From: Artem Bityutskiy To: "Kumar, Kaushlendra" , "rafael@kernel.org" , "lenb@kernel.org" Cc: "linux-pm@vger.kernel.org" Date: Tue, 11 Aug 2026 20:25:34 +0300 In-Reply-To: References: <20260811081729.186571-1-kaushlendra.kumar@intel.com> <9f75245a24905368dade4d172727933c4e1a74af.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-08-11 at 10:36 +0000, Kumar, Kaushlendra wrote: > On Tue, 2026-08-11 at 13:47 +0530, wrote: > > The current values are based on what I measured using wult/pbe tool. > >=20 > > I think it will be better to explain the problem and how this patch > > fixes it, give some details about workload. And ideally, also provided > > turbostat output when it runs in parallel with the workload before and > > after this patch. >=20 > Thank you for the feedback. >=20 > Looking at other platforms in intel_idle, C-state latency values are > generally sourced from BIOS ACPI _CST characterization data. For > example, MTL-L C6 (exit_latency=3D140, target_residency=3D420) and ADL-L > C6 (exit_latency=3D170, target_residency=3D500) match their respective > ACPI _CST tables. So there are platforms that have intel_idle table and that do not have it. > For PTL, I observed a discrepancy. The ACPI _CST on a Pantherlake-L > device reports: >=20 > C6S: latency=3D127us, residency=3D381us > C10: latency=3D1048us, residency=3D3144us Discrepancy -> difference. > Could you clarify which reference was used for other platforms =E2=80=94 = ACPI > _CST or wult =E2=80=94 so we can apply a consistent methodology for PTL? Platforms that do not have intel_idle custom table, use latency from ACPI _CST table. It only provides latency. Target residency is calculated as 3x latency. I do not know about _CST numbers. I only know that in many cases they are not what I can observe using wult tool. Panther Lake is the only client platform that I measured with the tools I developed, and submitted the numbers based on wult and pbe data that I got. Artem.