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[81.157.90.255]) by smtp.gmail.com with ESMTPSA id ck19-20020a5d5e93000000b00341c6440c36sm3898009wrb.74.2024.03.24.19.37.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 24 Mar 2024 19:37:27 -0700 (PDT) Date: Mon, 25 Mar 2024 02:37:26 +0000 From: Qais Yousef To: "Rafael J. Wysocki" Cc: Christian Loehle , linux-kernel@vger.kernel.org, peterz@infradead.org, juri.lelli@redhat.com, mingo@redhat.com, dietmar.eggemann@arm.com, vschneid@redhat.com, vincent.guittot@linaro.org, Johannes.Thumshirn@wdc.com, adrian.hunter@intel.com, ulf.hansson@linaro.org, andres@anarazel.de, asml.silence@gmail.com, linux-pm@vger.kernel.org, linux-block@vger.kernel.org, io-uring@vger.kernel.org Subject: Re: [RFC PATCH 2/2] cpufreq/schedutil: Remove iowait boost Message-ID: <20240325023726.itkhlg66uo5kbljx@airbuntu> References: <20240304201625.100619-1-christian.loehle@arm.com> <20240304201625.100619-3-christian.loehle@arm.com> <5060c335-e90a-430f-bca5-c0ee46a49249@arm.com> 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 Content-Transfer-Encoding: 8bit In-Reply-To: On 03/18/24 18:08, Rafael J. Wysocki wrote: > On Mon, Mar 18, 2024 at 5:40 PM Christian Loehle > wrote: > > > > On 18/03/2024 14:07, Rafael J. Wysocki wrote: > > > On Mon, Mar 4, 2024 at 9:17 PM Christian Loehle > > > wrote: > > >> > > >> The previous commit provides a new cpu_util_cfs_boost_io interface for > > >> schedutil which uses the io boosted utilization of the per-task > > >> tracking strategy. Schedutil iowait boosting is therefore no longer > > >> necessary so remove it. > > > > > > I'm wondering about the cases when schedutil is used without EAS. > > > > > > Are they still going to be handled as before after this change? > > > > Well they should still get boosted (under the new conditions) and according > > to my tests that does work. > > OK > > > Anything in particular you're worried about? > > It is not particularly clear to me how exactly the boost is taken into > account without EAS. > > > So in terms of throughput I see similar results with EAS and CAS+sugov. > > I'm happy including numbers in the cover letter for future versions, too. > > So far my intuition was that nobody would care enough to include them > > (as long as it generally still works). > > Well, IMV clear understanding of the changes is more important. I think the major thing we need to be careful about is the behavior when the task is sleeping. I think the boosting will be removed when the task is dequeued and I can bet there will be systems out there where the BLOCK softirq being boosted when the task is sleeping will matter. FWIW I do have an implementation for per-task iowait boost where I went a step further and converted intel_pstate too and like Christian didn't notice a regression. But I am not sure (rather don't think) I triggered this use case. I can't tell when the systems truly have per-cpu cpufreq control or just appear so and they are actually shared but not visible at linux level.