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[81.157.90.255]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-422f612800csm139712185e9.28.2024.06.16.14.48.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Jun 2024 14:48:14 -0700 (PDT) Date: Sun, 16 Jun 2024 22:48:12 +0100 From: Qais Yousef To: Lukasz Luba Cc: Kajetan Puchalski , rafael@kernel.org, daniel.lezcano@linaro.org, Dietmar.Eggemann@arm.com, dsmythies@telus.net, yu.chen.surf@gmail.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Ulf Hansson , Vincent Guittot , Todd Kjos , "wvw@google.com" Subject: Re: [PATCH v6 2/2] cpuidle: teo: Introduce util-awareness Message-ID: <20240616214812.nxtz2kt3svo44mbe@airbuntu> References: <20230105145159.1089531-1-kajetan.puchalski@arm.com> <20230105145159.1089531-3-kajetan.puchalski@arm.com> <20230711175814.zfavcn7xn3ia5va4@airbuntu> <20230718132432.w5xoxbqm54jmu6n5@airbuntu> <20230917010516.54dgcmms44wyfrvx@airbuntu> <20240529101950.bjpmmdqfhjg3aol6@airbuntu> Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 06/12/24 08:53, Lukasz Luba wrote: > > This won't help. We tried different values, unfortunately the logic is flawed. > > Utilization value on its own says nothing about the idleness of the system. > > This is not true. When you up-migrate a task to big CPU, then CPU idle > gov can instantly benefit from utilization information and won't make > mistake based on old local history and won't use deep idle state. > So migrating the utilization from one CPU to another CPU says a lot > about the idleness to that destination CPU. You can migrate a 1024 tasks to a bigger core, but it could run for 3ms and sleep for 40ms. So unfortunately I have to disagree with you here. Generally a high util value doesn't mean we are not going to be idle long enough to satisfy min_residency of the CPU. > When Christian removed the util he got -4.5% lower score in GB5, so > this util has impact [1]. We need the idle governor to help with power saving. We can disable DVFS and all idle states and always get a better performance. The residency is ~50% worse on some clusters with this change. Overall power impact is 2-4% in many use cases. GB5 is not really a representative use case to measure the usefulness of the idle governor. Task placement to avoid the cost of idle exit latency is a completely different problem.