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Date: Thu, 9 Aug 2018 16:55:53 +0100 From: Quentin Perret <quentin.perret@....com> To: Patrick Bellasi <patrick.bellasi@....com> Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>, "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, Viresh Kumar <viresh.kumar@...aro.org>, Vincent Guittot <vincent.guittot@...aro.org>, Paul Turner <pjt@...gle.com>, Dietmar Eggemann <dietmar.eggemann@....com>, Morten Rasmussen <morten.rasmussen@....com>, Juri Lelli <juri.lelli@...hat.com>, Todd Kjos <tkjos@...gle.com>, Joel Fernandes <joelaf@...gle.com>, Steve Muckle <smuckle@...gle.com>, Suren Baghdasaryan <surenb@...gle.com> Subject: Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks Hi Patrick, On Thursday 09 Aug 2018 at 16:41:56 (+0100), Patrick Bellasi wrote: > > IIUC, not far below this you should still have something like: > > > > if (rt_rq_is_runnable(&rq->rt)) > > return max; > > Do you mean that when RT tasks are RUNNABLE we still want to got to > MAX? Not sure to understand... since this patch is actually to clamp > the RT class... Argh, reading my message again it wasn't very clear indeed. Sorry about that ... What I'm try to say is that your patch does _not_ remove the snippet of code above from sugov_get_util(). So I think that when a RT task is runnable, you will not reach the end of the function where the clamping is done. And this is not what you want AFAICT. Does that make any sense ? > > > So you won't reach the actual clamping code at the end of the function > > when a RT task is runnable no? > > ... mmm... no... this patch is to clamp RT tasks... Am I missing > something? > > > Also, I always had the feeling that the default for RT should be > > util_min == 1024, and then users could decide to lower the bar if they > > want to. > > Mmm... good point! This would keep the policy unaltered for RT tasks. > > I want to keep sched class specific code in uclamp at minimum but > likely this should be achievable by just properly initializing the > task-specific util_min for RT tasks, if the original task has > UCLAM_NOT_VALID. +1, it'd be nice to keep the cross-class mess to a minimum IMO. But hopefully this RT thing isn't too ugly to implement ... > > > For the specific case of RT, that feels more natural than > > applying a max util clamp IMO. What do you think ? > > I'll look better into this for the next posting! Sounds good :-) Thanks, Quentin
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