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Date: Thu, 16 Apr 2020 19:23:31 +0200 From: Dietmar Eggemann <dietmar.eggemann@....com> To: Joel Fernandes <joel@...lfernandes.org>, Qais Yousef <qais.yousef@....com> Cc: Peter Zijlstra <peterz@...radead.org>, Patrick Bellasi <patrick.bellasi@....com>, Subhra Mazumdar <subhra.mazumdar@...cle.com>, linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de, steven.sistare@...cle.com, dhaval.giani@...cle.com, daniel.lezcano@...aro.org, vincent.guittot@...aro.org, viresh.kumar@...aro.org, tim.c.chen@...ux.intel.com, mgorman@...hsingularity.net, parth@...ux.ibm.com Subject: Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice Hi Joel, On 16.04.20 02:02, Joel Fernandes wrote: > On Thu, Sep 05, 2019 at 12:47:26PM +0100, Qais Yousef wrote: >> On 09/05/19 13:30, Peter Zijlstra wrote: >>> On Thu, Sep 05, 2019 at 12:13:47PM +0100, Qais Yousef wrote: >>>> On 09/05/19 12:46, Peter Zijlstra wrote: >>> >>>>> This is important because we want to be able to bias towards less >>>>> importance to (tail) latency as well as more importantance to (tail) >>>>> latency. >>>>> >>>>> Specifically, Oracle wants to sacrifice (some) latency for throughput. >>>>> Facebook OTOH seems to want to sacrifice (some) throughput for latency. >>>> >>>> Another use case I'm considering is using latency-nice to prefer an idle CPU if >>>> latency-nice is set otherwise go for the most energy efficient CPU. >>>> >>>> Ie: sacrifice (some) energy for latency. >>>> >>>> The way I see interpreting latency-nice here as a binary switch. But >>>> maybe we can use the range to select what (some) energy to sacrifice >>>> mean here. Hmmm. >>> >>> It cannot be binary, per definition is must be ternary, that is, <0, ==0 >>> and >0 (or middle value if you're of that persuasion). >> >> I meant I want to use it as a binary. >> >>> >>> In your case, I'm thinking you mean >0, we want to lower the latency. >> >> Yes. As long as there's an easy way to say: does this task care about latency >> or not I'm good. > > Qais, Peter, all, > > For ChromeOS (my team), we are planning to use the upstream uclamp mechanism > instead of the out-of-tree schedtune mechanism to provide EAS with the > latency-sensitivity (binary/ternary) hint. ChromeOS is thankfully quite a bit > upstream focussed :) > > However, uclamp is missing an attribute to provide this biasing to EAS as we > know. > > What was the consensus on adding a per-task attribute to uclamp for providing > this? Happy to collaborate on this front. We're planning to have a session about this topic (latency-nice attribute per task group) during the virtual Pisa OSPM summit retis.sssup.it/ospm-summit in May this year. There are two presentations/discussions planned: "Introducing Latency Nice for Scheduler Hints and Optimizing Scheduler Task Wakeup" and "The latency nice use case for Energy-Aware-Scheduling (EAS) in Android Common Kernel (ACK)" We'll probably merge those two into one presentation/discussion. So far we have Parth's per-task implementation https://lore.kernel.org/lkml/20200228090755.22829-1-parth@linux.ibm.com What's missing is the per-taskgroup implementation, at least from the standpoint of ACK. The (mainline) EAS use-case for latency nice is already in ACK (android-5.4): https://android.googlesource.com/kernel/common/+/760b82c9b88d2c8125abfc5f732cc3cd460b2a54
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