linux-kernel - Re: [PATCH v4 00/10] sched/fair: rework the CFS load balance

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Date:   Fri, 3 Jan 2020 16:39:08 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org
Cc:     pauld@...hat.com, srikar@...ux.vnet.ibm.com,
        quentin.perret@....com, dietmar.eggemann@....com,
        Morten.Rasmussen@....com, hdanton@...a.com, parth@...ux.ibm.com,
        riel@...riel.com
Subject: Re: [PATCH v4 00/10] sched/fair: rework the CFS load balance

On 25/11/2019 12:48, Valentin Schneider wrote:
> I've been busy trying to get some perf numbers on arm64 server~ish systems,
> I finally managed to get some specjbb numbers on TX2 (the 2 nodes, 224
> CPUs version which I suspect is the same as you used in the above). I only
> have a limited number of iterations (5, although each runs for about 2h)
> because I wanted to get some (usable) results by today, I'll spin some more
> during the week.
> 
> 
> This is based on the "critical-jOPs" metric which AFAIU higher is better:
> 
> Baseline, SMTOFF:
>   mean     12156.400000
>   std        660.640068
>   min      11016.000000
>   25%      12158.000000
>   50%      12464.000000
>   75%      12521.000000
>   max      12623.000000
> 
> Patches (+ find_idlest_group() fixup), SMTOFF:
>   mean     12487.250000
>   std        184.404221
>   min      12326.000000
>   25%      12349.250000
>   50%      12449.500000
>   75%      12587.500000
>   max      12724.000000	
> 
> 
> It looks slightly better overall (mean, stddev), but I'm annoyed by that
> low iteration count. I also had some issues with my SMTON run and I only
> got numbers for 2 iterations, so I'll respin that before complaining.
> 
> FWIW the branch I've been using is:
> 
>   http://www.linux-arm.org/git?p=linux-vs.git;a=shortlog;h=refs/heads/mainline/load-balance/vincent_rework/tip
> 

Forgot about that; I got some more results in the meantime, still specjbb
and still ThunderX2):

| kernel          | count |         mean |        std |     min |     50% |      75% |      99% |     max |
|-----------------+-------+--------------+------------+---------+---------+----------+----------+---------|
| -REWORK SMT-ON  |    15 | 19961.133333 | 613.406515 | 19058.0 | 20006.0 | 20427.50 | 20903.42 | 20924.0 |
| +REWORK SMT-ON  |    12 | 19265.666667 | 563.959917 | 18380.0 | 19133.5 | 19699.25 | 20024.90 | 20026.0 |
| -REWORK SMT-OFF |    25 | 12397.000000 | 425.763628 | 11016.0 | 12377.0 | 12623.00 | 13137.20 | 13154.0 |
| +REWORK SMT-OFF |    20 | 12436.700000 | 414.130554 | 11313.0 | 12505.0 | 12687.00 | 12981.44 | 12986.0 |

SMT-ON  delta: -3.48%
SMT-OFF delta: +0.32%


This is consistent with some earlier runs (where I had a few issues
getting enough iterations): SMT-OFF performs a tad better, and SMT-ON
performs slightly worse.

Looking at the 99th percentile, it seems we're a bit worse compared to
the previous best cases, but looking at the slightly reduced stddev it also
seems that we are somewhat more consistent.