Messages in this thread | | | Subject | Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice | From | Parth Shah <> | Date | Mon, 20 Apr 2020 16:56:55 +0530 |
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Hi Joel,
On 4/18/20 9:31 PM, Joel Fernandes wrote: > Hi Dietmar, > > On Thu, Apr 16, 2020 at 1:23 PM Dietmar Eggemann > <dietmar.eggemann@arm.com> wrote: >> >> 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. > > Cool, I registered as well. > >> >> 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 > > Cool, I see it has some Reviewed-by tags so that's a good sign. Will > look more into that. > >> 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 > > Yes, I was aware of this. But if we use task groups, then the > transition from schedtune -> uclamp means now the tasks that use > uclamp would also be subjected to cpu.shares. That's why we were > looking into the per-task interface and glad there's some work on this > already done. >
Yes, that series of latency_nice seems to be in good shape to be used for any usecases. Hopefully, OSPM will lead to its upstreaming sooner :-) But at the end, we aim to have both the per-task and cgroup based interface to mark the latency_nice value of a task. Till, then I'm finding some generic use-cases to show benefits of such task attribute to increase community interest.
Thanks, Parth
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