linux-kernel - Re: [PATCH] sched/fair: Do not decay new task load on first enqueue

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Message-ID: <20161018102937.GI16071@codeblueprint.co.uk>
Date:   Tue, 18 Oct 2016 11:29:37 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Wanpeng Li <kernellwp@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Yuyang Du <yuyang.du@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH] sched/fair: Do not decay new task load on first enqueue

On Tue, 11 Oct, at 11:24:53AM, Matt Fleming wrote:
> 
> That's a lot more costly cross-DIE migrations. I think this patch is
> along the right lines, but there's something fishy happening on this
> box.

I wasn't really able to track down why this machine regressed, and the
patch shows enough improvement for other boxes that I think it's worth
sticking in tip/sched/core.

I saw a number of double digit gains for hackbench with this patch.
Here's a 4-cpu box that shows improvements in arithmetic mean and some
nice improvements to the stddev,

hackbench-process-pipes
                            4.8.0                 4.8.0
                          vanilla  find-idle-group-v1r1
Amean    1       3.2580 (  0.00%)      3.0607 (  6.06%)
Amean    3       8.0387 (  0.00%)      8.2027 ( -2.04%)
Amean    5      12.0507 (  0.00%)     12.1703 ( -0.99%)
Amean    7      16.0027 (  0.00%)     16.4567 ( -2.84%)
Amean    12     26.9030 (  0.00%)     21.7767 ( 19.05%)
Amean    16     33.4127 (  0.00%)     28.9877 ( 13.24%)
Stddev   1       0.1383 (  0.00%)      0.1787 (-29.22%)
Stddev   3       0.1297 (  0.00%)      0.1677 (-29.29%)
Stddev   5       0.5495 (  0.00%)      0.4549 ( 17.22%)
Stddev   7       0.7401 (  0.00%)      0.6161 ( 16.75%)
Stddev   12      2.3187 (  0.00%)      0.7102 ( 69.37%)
Stddev   16      4.0734 (  0.00%)      2.9364 ( 27.91%)

And a 60-cpu box with similar improvements,

hackbench-process-sockets
                             4.8.0                 4.8.0
                           vanilla  find-idle-group-v1r1
Amean    1       32.8810 (  0.00%)      2.0590 ( 93.74%)
Amean    4       34.8663 (  0.00%)      3.3177 ( 90.48%)
Amean    7       34.1243 (  0.00%)      4.3323 ( 87.30%)
Amean    12      36.8373 (  0.00%)      5.3650 ( 85.44%)
Amean    21      29.0333 (  0.00%)      6.0280 ( 79.24%)
Amean    30      27.2807 (  0.00%)      7.2653 ( 73.37%)
Amean    48      23.2453 (  0.00%)      9.9810 ( 57.06%)
Amean    79      29.6660 (  0.00%)     16.6680 ( 43.81%)
Amean    110     41.3680 (  0.00%)     23.1787 ( 43.97%)
Amean    141     45.3720 (  0.00%)     29.4130 ( 35.17%)
Amean    172     45.6403 (  0.00%)     34.3783 ( 24.68%)
Amean    203     47.6120 (  0.00%)     40.0063 ( 15.97%)
Amean    234     50.1703 (  0.00%)     43.4503 ( 13.39%)
Amean    240     50.1110 (  0.00%)     44.4660 ( 11.26%)
Stddev   1        0.9714 (  0.00%)      0.6617 ( 31.88%)
Stddev   4        0.4459 (  0.00%)      0.2943 ( 34.01%)
Stddev   7        0.3091 (  0.00%)      0.2722 ( 11.94%)
Stddev   12       0.4603 (  0.00%)      0.1424 ( 69.05%)
Stddev   21       1.3647 (  0.00%)      0.1566 ( 88.52%)
Stddev   30       4.1277 (  0.00%)      0.0481 ( 98.84%)
Stddev   48       1.3689 (  0.00%)      0.4968 ( 63.71%)
Stddev   79       2.0772 (  0.00%)      0.5309 ( 74.44%)
Stddev   110      4.5655 (  0.00%)      0.1846 ( 95.96%)
Stddev   141      4.2637 (  0.00%)      0.6675 ( 84.34%)
Stddev   172      1.5741 (  0.00%)      1.0242 ( 34.93%)
Stddev   203      1.0973 (  0.00%)      1.4043 (-27.98%)
Stddev   234      2.2048 (  0.00%)      0.8709 ( 60.50%)
Stddev   240      1.2849 (  0.00%)      0.2688 ( 79.08%)