From: Peter Zijlstra <peterz@infradead.org> To: Patrick Bellasi <patrick.bellasi@arm.com> Cc: Juri Lelli <juri.lelli@redhat.com>, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>, "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>, Viresh Kumar <viresh.kumar@linaro.org>, Vincent Guittot <vincent.guittot@linaro.org>, Paul Turner <pjt@google.com>, Quentin Perret <quentin.perret@arm.com>, Dietmar Eggemann <dietmar.eggemann@arm.com>, Morten Rasmussen <morten.rasmussen@arm.com>, Todd Kjos <tkjos@google.com>, Joel Fernandes <joelaf@google.com>, Steve Muckle <smuckle@google.com>, Suren Baghdasaryan <surenb@google.com> Subject: Re: [PATCH v4 14/16] sched/core: uclamp: request CAP_SYS_ADMIN by default Date: Mon, 24 Sep 2018 18:26:40 +0200 Message-ID: <20180924162640.GB7060@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20180924151400.GT1413@e110439-lin> On Mon, Sep 24, 2018 at 04:14:00PM +0100, Patrick Bellasi wrote: > ... still it's difficult to give a precise definition of knee point, > unless you know about platforms which have a sharp change in energy > efficiency. > > The only cases we know about are those where: > > A) multiple frequencies uses the same voltage, e.g. > > > ^ * > | Energy O > | efficiency O+ > | O | > | O* | > | O** | > | O** O*** | > | + O** O**** | > | | O** O***** | > | | O** | > | | + | > | | Same V | Increasing V | > +---+----------+----------------------+-----------> > | | | Frequency > L M H > > B) there is a big frequency gap between low frequency OPPs and high > frequency OPPs, e.g. > > O > ^ **+ > | Energy ** | > | efficiency ** | > | ** | > | ** | > | ** | > | ** | > | ** | > | O** | > | O******+ | > |O******* | | > | | | > ++--------------+------------------+------> > | | | Frequency > L M H > > > In case A, all the OPPs left of M are dominated by M in terms > of energy efficiency and normally they should be never used. > Unless you are under thermal constraints and you still want to keep > your code running even if at a lower rate and energy efficiency. > At this point, however, you already invalidated all the OPPs right of > M and, on the remaining, you still struggle do define the knee point. > > In case B... I'm wondering it such a conf even makes sense ;) > Is there really some platform out there with such a "non homogeneously > distributed" set of available frequencies ? Well, the curve is a second or third order polynomial (when V~f -> fV^2 -> f^3), so it shoots up at some point. There's not really anything you can do about that. But if you're willing to put in active cooling and lots of energy, you can make it go fast :-) Therefore I was thinking: > Maybe we can define a threshold > for a "EE derivative ratio", but it will still be quite arbitrary. Because up until de/df=.5 we gain more performance than we loose ee. But I might not have appreciated the fact that when we work with imaginary cost units that skews the .5.
next prev parent reply index Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-08-28 13:53 [PATCH v4 00/16] Add utilization clamping support Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 01/16] sched/core: uclamp: extend sched_setattr to support utilization clamping Patrick Bellasi 2018-09-05 11:01 ` Juri Lelli 2018-08-28 13:53 ` [PATCH v4 02/16] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Patrick Bellasi 2018-09-05 10:45 ` Juri Lelli 2018-09-06 13:48 ` Patrick Bellasi 2018-09-06 14:13 ` Juri Lelli 2018-09-06 8:17 ` Juri Lelli 2018-09-06 14:00 ` Patrick Bellasi 2018-09-08 23:47 ` Suren Baghdasaryan 2018-09-12 10:32 ` Patrick Bellasi 2018-09-12 13:49 ` Peter Zijlstra 2018-09-12 15:56 ` Patrick Bellasi 2018-09-12 16:12 ` Peter Zijlstra 2018-09-12 17:35 ` Patrick Bellasi 2018-09-12 17:42 ` Peter Zijlstra 2018-09-12 17:52 ` Patrick Bellasi 2018-09-13 19:14 ` Peter Zijlstra 2018-09-14 8:51 ` Patrick Bellasi 2018-09-12 16:24 ` Peter Zijlstra 2018-09-12 17:42 ` Patrick Bellasi 2018-09-13 19:20 ` Peter Zijlstra 2018-09-14 8:47 ` Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 03/16] sched/core: uclamp: add CPU's clamp groups accounting Patrick Bellasi 2018-09-12 17:34 ` Peter Zijlstra 2018-09-12 17:44 ` Patrick Bellasi 2018-09-13 19:12 ` Peter Zijlstra 2018-09-14 9:07 ` Patrick Bellasi 2018-09-14 11:52 ` Peter Zijlstra 2018-09-14 13:41 ` Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 04/16] sched/core: uclamp: update CPU's refcount on clamp changes Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 05/16] sched/core: uclamp: enforce last task UCLAMP_MAX Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 06/16] sched/cpufreq: uclamp: add utilization clamping for FAIR tasks Patrick Bellasi 2018-09-14 9:32 ` Peter Zijlstra 2018-09-14 13:19 ` Patrick Bellasi 2018-09-14 13:36 ` Peter Zijlstra 2018-09-14 13:57 ` Patrick Bellasi 2018-09-27 10:23 ` Quentin Perret 2018-08-28 13:53 ` [PATCH v4 07/16] sched/core: uclamp: extend cpu's cgroup controller Patrick Bellasi 2018-08-28 18:29 ` Randy Dunlap 2018-08-29 8:53 ` Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 08/16] sched/core: uclamp: propagate parent clamps Patrick Bellasi 2018-09-09 3:02 ` Suren Baghdasaryan 2018-09-12 12:51 ` Patrick Bellasi 2018-09-12 15:56 ` Suren Baghdasaryan 2018-09-11 15:18 ` Tejun Heo 2018-09-11 16:26 ` Patrick Bellasi 2018-09-11 16:28 ` Tejun Heo 2018-08-28 13:53 ` [PATCH v4 09/16] sched/core: uclamp: map TG's clamp values into CPU's clamp groups Patrick Bellasi 2018-09-09 18:52 ` Suren Baghdasaryan 2018-09-12 14:19 ` Patrick Bellasi 2018-09-12 15:53 ` Suren Baghdasaryan 2018-08-28 13:53 ` [PATCH v4 10/16] sched/core: uclamp: use TG's clamps to restrict Task's clamps Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 11/16] sched/core: uclamp: add system default clamps Patrick Bellasi 2018-09-10 16:20 ` Suren Baghdasaryan 2018-09-11 16:46 ` Patrick Bellasi 2018-09-11 19:25 ` Suren Baghdasaryan 2018-08-28 13:53 ` [PATCH v4 12/16] sched/core: uclamp: update CPU's refcount on TG's clamp changes Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 13/16] sched/core: uclamp: use percentage clamp values Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 14/16] sched/core: uclamp: request CAP_SYS_ADMIN by default Patrick Bellasi 2018-09-04 13:47 ` Juri Lelli 2018-09-06 14:40 ` Patrick Bellasi 2018-09-06 14:59 ` Juri Lelli 2018-09-06 17:21 ` Patrick Bellasi 2018-09-14 11:10 ` Peter Zijlstra 2018-09-14 14:07 ` Patrick Bellasi 2018-09-14 14:28 ` Peter Zijlstra 2018-09-17 12:27 ` Patrick Bellasi 2018-09-21 9:13 ` Peter Zijlstra 2018-09-24 15:14 ` Patrick Bellasi 2018-09-24 15:56 ` Peter Zijlstra 2018-09-24 17:23 ` Patrick Bellasi 2018-09-24 16:26 ` Peter Zijlstra [this message] 2018-09-24 17:19 ` Patrick Bellasi 2018-09-25 15:49 ` Peter Zijlstra 2018-09-26 10:43 ` Patrick Bellasi 2018-09-27 10:00 ` Quentin Perret 2018-09-26 17:51 ` Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 15/16] sched/core: uclamp: add clamp group discretization support Patrick Bellasi 2018-08-28 13:53 ` [PATCH v4 16/16] sched/cpufreq: uclamp: add utilization clamping for RT tasks Patrick Bellasi
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