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Message-ID: <CAKfTPtA9DYJ5=VYGpS_XBzzmvgJeYcmmG261A1cby_sT7kHdYg@mail.gmail.com>
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,
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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.
>
>
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