linux-kernel - Re: [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr

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Date:   Mon, 16 Oct 2023 18:50:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Youssef Esmat <youssefesmat@...omium.org>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>, mingo@...nel.org,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, corbet@....net, qyousef@...alina.io,
        chris.hyser@...cle.com, patrick.bellasi@...bug.net, pjt@...gle.com,
        pavel@....cz, qperret@...gle.com, tim.c.chen@...ux.intel.com,
        joshdon@...gle.com, timj@....org, kprateek.nayak@....com,
        yu.c.chen@...el.com, joel@...lfernandes.org, efault@....de,
        tglx@...utronix.de
Subject: Re: [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr


Sorry, I seem to have forgotten to reply to this part...

On Mon, Oct 09, 2023 at 07:51:03PM -0500, Youssef Esmat wrote:

> I think looking at the sched latency numbers alone does not show the
> complete picture. I ran the same input latency test again and tried to
> capture some of these numbers for the chrome processes.
> 
> EEVDF 1.5ms slice:
> 
> Input latency test result: 226ms
> perf sched latency:
> switches: 1,084,694
> avg:   1.139 ms
> max: 408.397 ms
> 
> EEVDF 6.0ms slice:
> 
> Input latency test result: 178ms
> perf sched latency:
> switches: 892,306
> avg:   1.145 ms
> max: 354.344 ms

> For our scenario, it is very expensive to interrupt UI threads. It
> will increase the input latency significantly. Lowering the scheduling
> latency at the cost of switching out important threads can be very
> detrimental in this workload. UI and input threads run with a nice
> value of -8.

> That said, this might not be beneficial for all workloads, and we are
> still trying our other workloads out.

Right, this seems to suggest something on your critical path (you should
trace that) has more than 3ms of compute in a single activation. 

Basically this means chrome is fairly fat on this critical path. But it
seems you know about that.

Anyway, once you know the 95% length of the longest activation on your
critical path, you can indeed set your slice to that. This should be
readily available from trace data.