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[2603:800c:1a02:1bae:a7fa:157f:969a:4cde]) by smtp.gmail.com with ESMTPSA id 9-20020a621409000000b0053e6eae9668sm2417284pfu.2.2022.09.21.09.48.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Sep 2022 09:48:45 -0700 (PDT) Sender: Tejun Heo Date: Wed, 21 Sep 2022 06:48:43 -1000 From: Tejun Heo To: Qais Yousef Cc: Vincent Guittot , Dietmar Eggemann , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, parth@linux.ibm.com, chris.hyser@oracle.com, valentin.schneider@arm.com, patrick.bellasi@matbug.net, David.Laight@aculab.com, pjt@google.com, pavel@ucw.cz, qperret@google.com, tim.c.chen@linux.intel.com, joshdon@google.com Subject: Re: [PATCH v4 6/8] sched/fair: Add sched group latency support Message-ID: References: <20220916080305.29574-1-vincent.guittot@linaro.org> <20220916080305.29574-7-vincent.guittot@linaro.org> <000c2893-feb4-373d-2234-2ca74be94714@arm.com> <20220921155521.qb3jb74nbjoenau6@airbuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220921155521.qb3jb74nbjoenau6@airbuntu> X-Spam-Status: No, score=-1.5 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Wed, Sep 21, 2022 at 05:07:38PM +0100, Qais Yousef wrote: > Wouldn't cpu.latency.nice be enough? I think the latency_offset is > implementation detail that userspace shouldn't be concerned about. One option could be just using the same mapping as cpu.weight so that 100 maps to neutral, 10000 maps close to -20, 1 maps close to 19. It isn't great that the value can't be interpreted in any intuitive way (e.g. a time duration based interface would be a lot easier to grok even if it still is best effort) but if that's what the per-task interface is gonna be, it'd be best to keep cgroup interface in line. As for whether a single value would fit the bill, it's again something which should be answered for both task and cgroup based interface at the same time. That said, my not-too-throught-through opinion is that a single value for per-task / per-cgroup interface + system level knobs to fine tune how that actually applies is likely enough and probably better than exposing exposing a host of internal details to applications directly. Thanks. -- tejun