linux-kernel - Re: [PATCH 00/10] sched: EEVDF using latency-nice

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Date:   Tue, 7 Mar 2023 11:27:37 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.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, youssefesmat@...omium.org,
        joel@...lfernandes.org
Subject: Re: [PATCH 00/10] sched: EEVDF using latency-nice

On Mon, 6 Mar 2023 at 15:17, Peter Zijlstra <peterz@...radead.org> wrote:
>
> Hi!
>
> Ever since looking at the latency-nice patches, I've wondered if EEVDF would
> not make more sense, and I did point Vincent at some older patches I had for
> that (which is here his augmented rbtree thing comes from).
>
> Also, since I really dislike the dual tree, I also figured we could dynamically
> switch between an augmented tree and not (and while I have code for that,
> that's not included in this posting because with the current results I don't
> think we actually need this).
>
> Anyway, since I'm somewhat under the weather, I spend last week desperately
> trying to connect a small cluster of neurons in defiance of the snot overlord
> and bring back the EEVDF patches from the dark crypts where they'd been
> gathering cobwebs for the past 13 odd years.

I haven't studied your patchset in detail yet but at a 1st glance this
seems to be a major rework on the cfs task placement and the latency
is just an add-on on top of moving to the EEVDF scheduling.

>
> By friday they worked well enough, and this morning (because obviously I forgot
> the weekend is ideal to run benchmarks) I ran a bunch of hackbenck, netperf,
> tbench and sysbench -- there's a bunch of wins and losses, but nothing that
> indicates a total fail.
>
> ( in fact, some of the schbench results seem to indicate EEVDF schedules a lot
>   more consistent than CFS and has a bunch of latency wins )
>
> ( hackbench also doesn't show the augmented tree and generally more expensive
>   pick to be a loss, in fact it shows a slight win here )
>
>
>   hackbech load + cyclictest --policy other results:
>
>
>                         EEVDF                    CFS
>
>                 # Min Latencies: 00053
>   LNICE(19)     # Avg Latencies: 04350
>                 # Max Latencies: 76019
>
>                 # Min Latencies: 00052          00053
>   LNICE(0)      # Avg Latencies: 00690          00687
>                 # Max Latencies: 14145          13913
>
>                 # Min Latencies: 00019
>   LNICE(-19)    # Avg Latencies: 00261
>                 # Max Latencies: 05642
>
>
> The nice -19 numbers aren't as pretty as Vincent's, but at the end I was going
> cross-eyed from staring at tree prints and I just couldn't figure out where it
> was going side-ways.
>
> There's definitely more benchmarking/tweaking to be done (0-day already
> reported a stress-ng loss), but if we can pull this off we can delete a whole
> much of icky heuristics code. EEVDF is a much better defined policy than what
> we currently have.
>
>