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Date:   Tue, 15 Dec 2020 20:41:29 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Valentin Schneider <valentin.schneider@....com>,
        Qais Yousef <qais.yousef@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...e.de>, Jiang Biao <benbjiang@...il.com>
Subject: Re: [RFC PATCH v8] sched/fair: select idle cpu from idle cpumask for
 task wakeup

Hi Bao Hua,

Sorry I almost missed this message, :(

On 2020/12/14 7:29, Song Bao Hua (Barry Song) wrote:
> 
> Hi Aubrey,
> 
> The patch looks great. But I didn't find any hackbench improvement
> on kunpeng 920 which has 24 cores for each llc span. Llc span is also
> one numa node. The topology is like:
> # numactl --hardware
> available: 4 nodes (0-3)
> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
> node 0 size: 128669 MB
> node 0 free: 126995 MB
> node 1 cpus: 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
> 43 44 45 46 47
> node 1 size: 128997 MB
> node 1 free: 127539 MB
> node 2 cpus: 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
> 67 68 69 70 71
> node 2 size: 129021 MB
> node 2 free: 127106 MB
> node 3 cpus: 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90
> 91 92 93 94 95
> node 3 size: 127993 MB
> node 3 free: 126739 MB
> node distances:
> node   0   1   2   3
>   0:  10  12  20  22
>   1:  12  10  22  24
>   2:  20  22  10  12
>   3:  22  24  12  10
> 
> Benchmark command:
> numactl -N 0-1 hackbench -p -T -l 20000 -g $1
> 
> for each g, I ran 10 times to get the average time. And I tested
> g from 1 to 10.
> 
> g     1      2      3      4      5      6       7     8        9       10
> w/o   1.4733 1.5992 1.9353 2.1563 2.8448 3.3305 3.9616 4.4870 5.0786 5.6983
> w/    1.4709 1.6152 1.9474 2.1512 2.8298 3.2998 3.9472 4.4803 5.0462 5.6505
> 
> Is it because the core number is small in llc span in my test?

I guess it is with SIS_PROP, when the system is very busy that idle cpu scan
loop is throttled by nr(4). The patch actually reduces 4 times scan so the
data change looks marginal. Vincent mentioned a notable change at here:
	
	https://lkml.org/lkml/2020/12/14/109

Maybe you can increase the group number to see if it can be reproduced on
your side.

Thanks,
-Aubrey

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