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[2003:ef:2bd3:1703:fe36:7972:448a:ed7a]) by smtp.gmail.com with ESMTPSA id n12-v6sm659244wrm.62.2018.08.07.02.59.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 07 Aug 2018 02:59:07 -0700 (PDT) Date: Tue, 7 Aug 2018 11:59:05 +0200 From: Juri Lelli To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Dietmar Eggemann , Morten Rasmussen , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan Subject: Re: [PATCH v3 01/14] sched/core: uclamp: extend sched_setattr to support utilization clamping Message-ID: <20180807095905.GB2288@localhost.localdomain> References: <20180806163946.28380-1-patrick.bellasi@arm.com> <20180806163946.28380-2-patrick.bellasi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180806163946.28380-2-patrick.bellasi@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Minor comments below. On 06/08/18 17:39, Patrick Bellasi wrote: [...] > + * > + * Task Utilization Attributes > + * =========================== > + * > + * A subset of sched_attr attributes allows to specify the utilization which > + * should be expected by a task. These attributes allows to inform the ^ allow > + * scheduler about the utilization boundaries within which is safe to schedule Isn't all this more about providing hints than safety? > + * the task. These utilization boundaries are valuable information to support > + * scheduler decisions on both task placement and frequencies selection. > + * > + * @sched_util_min represents the minimum utilization > + * @sched_util_max represents the maximum utilization > + * > + * Utilization is a value in the range [0..SCHED_CAPACITY_SCALE] which > + * represents the percentage of CPU time used by a task when running at the > + * maximum frequency on the highest capacity CPU of the system. Thus, for > + * example, a 20% utilization task is a task running for 2ms every 10ms. > + * > + * A task with a min utilization value bigger then 0 is more likely to be > + * scheduled on a CPU which can provide that bandwidth. > + * A task with a max utilization value smaller then 1024 is more likely to be > + * scheduled on a CPU which do not provide more then the required bandwidth. Isn't s/bandwidth/capacity/ here, above, and in general where you use the term "bandwidth" more appropriate? I wonder if overloading this term (w.r.t. how is used with DEADLINE) might create confusion. In this case we are not providing any sort of guarantees, it's a hint. Best, - Juri