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Date: Sun, 27 Feb 2022 11:02:09 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Tim Chen <tim.c.chen@...el.com>, linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Barry Song <21cnbao@...il.com>,
Barry Song <song.bao.hua@...ilicon.com>,
Yicong Yang <yangyicong@...ilicon.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Aubrey Li <aubrey.li@...el.com>,
Len Brown <len.brown@...el.com>,
Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH][RFC] sched: Stop searching for idle cpu if the LLC
domain is overloaded
Hi Prateek,
On Wed, Feb 23, 2022 at 03:35:35PM +0530, K Prateek Nayak wrote:
> Hello Chenyu,
>
> On 2/7/2022 9:10 AM, Chen Yu wrote:
> > [Problem Statement]
> > Searching for an idle cpu/core in a LLC domain is time consuming
> > when the LLC domain is relatively busy. Even worse, it is possible
> > that after iterating the whole LLC domain, it might still
> > fail to find an idle cpu/core.
>
> We tested the patch running some standard benchmark on a dual
> socket AMD Zen3 system (2 x 64C/128T). Following are the results
> comparing the results seen on tip/sched/core (sched-tip) and
> tip/sched/core + this patch (util-avg)
>
> ~~~~~~~~~
> hackbench
> ~~~~~~~~~
>
> NPS Mode - NPS1
> Test: sched-tip util-avg
> 1-groups: 4.97 (0.00 pct) 5.06 (-1.81 pct)
> 2-groups: 5.71 (0.00 pct) 5.65 (1.05 pct)
> 4-groups: 6.33 (0.00 pct) 6.22 (1.73 pct)
> 8-groups: 7.93 (0.00 pct) 7.77 (2.01 pct)
> 16-groups: 12.35 (0.00 pct) 11.75 (4.85 pct)
>
> NPS Mode - NPS2
> Test: sched-tip util-avg
> 1-groups: 4.87 (0.00 pct) 4.97 (-2.05 pct)
> 2-groups: 5.43 (0.00 pct) 5.39 (0.73 pct)
> 4-groups: 6.07 (0.00 pct) 5.94 (2.14 pct)
> 8-groups: 7.46 (0.00 pct) 7.39 (0.93 pct)
> 16-groups: 10.27 (0.00 pct) 10.07 (1.94 pct)
>
> NPS Mode - NPS4
> Test: sched-tip util-avg
> 1-groups: 4.87 (0.00 pct) 4.89 (-0.41 pct)
> 2-groups: 5.40 (0.00 pct) 5.48 (-1.48 pct)
> 4-groups: 6.15 (0.00 pct) 6.17 (-0.32 pct)
> 8-groups: 7.63 (0.00 pct) 7.53 (1.31 pct)
> 16-groups: 10.24 (0.00 pct) 9.89 (3.41 pct)
>
> ~~~~~~~~
> schbench
> ~~~~~~~~
>
> NPS Mode - NPS1
> #workers: sched-tip util-avg
> 1: 13.00 (0.00 pct) 14.50 (-11.53 pct)
> 2: 31.50 (0.00 pct) 34.00 (-7.93 pct)
> 4: 43.50 (0.00 pct) 37.50 (13.79 pct)
> 8: 56.00 (0.00 pct) 50.50 (9.82 pct)
> 16: 69.50 (0.00 pct) 68.50 (1.43 pct)
> 32: 107.00 (0.00 pct) 106.50 (0.46 pct)
> 64: 191.00 (0.00 pct) 191.50 (-0.26 pct)
> 128: 413.50 (0.00 pct) 408.50 (1.20 pct)
> 256: 950.00 (0.00 pct) 947.00 (0.31 pct)
> 512: 60352.00 (0.00 pct) 60288.00 (0.10 pct)
>
> NPS Mode - NPS2
> #workers: sched-tip util-avg
> 1: 11.50 (0.00 pct) 11.00 (4.34 pct)
> 2: 26.00 (0.00 pct) 30.00 (-15.38 pct)
> 4: 36.00 (0.00 pct) 39.00 (-8.33 pct)
> 8: 57.50 (0.00 pct) 49.50 (13.91 pct)
> 16: 68.50 (0.00 pct) 69.00 (-0.72 pct)
> 32: 105.50 (0.00 pct) 104.50 (0.94 pct)
> 64: 192.50 (0.00 pct) 189.50 (1.55 pct)
> 128: 403.50 (0.00 pct) 430.00 (-6.56 pct)
> 256: 945.00 (0.00 pct) 957.00 (-1.26 pct)
> 512: 60288.00 (0.00 pct) 60224.00 (0.10 pct)
>
> NPS Mode - NPS4
> #workers: sched-tip util-avg
> 1: 12.50 (0.00 pct) 11.50 (8.00 pct)
> 2: 29.00 (0.00 pct) 23.00 (20.68 pct)
> 4: 28.50 (0.00 pct) 29.50 (-3.50 pct)
> 8: 45.00 (0.00 pct) 46.50 (-3.33 pct)
> 16: 74.00 (0.00 pct) 84.00 (-13.51 pct)
> 32: 110.50 (0.00 pct) 108.50 (1.80 pct)
> 64: 198.00 (0.00 pct) 191.50 (3.28 pct)
> 128: 434.00 (0.00 pct) 418.00 (3.68 pct)
> 256: 964.00 (0.00 pct) 952.00 (1.24 pct)
> 512: 60352.00 (0.00 pct) 60352.00 (0.00 pct)
>
> ~~~~~~
> tbench
> ~~~~~~
>
> NPS Mode - NPS1
> Clients: sched-tip util-avg
> 1 475.40 (0.00 pct) 480.46 (1.06 pct)
> 2 939.62 (0.00 pct) 929.13 (-1.11 pct)
> 4 1767.75 (0.00 pct) 1798.94 (1.76 pct)
> 8 3315.70 (0.00 pct) 3231.78 (-2.53 pct)
> 16 5887.79 (0.00 pct) 6037.36 (2.54 pct)
> 32 10202.20 (0.00 pct) 10223.65 (0.21 pct)
> 64 16816.42 (0.00 pct) 17122.40 (1.81 pct)
> 128 28423.90 (0.00 pct) 28680.46 (0.90 pct)
> 256 26726.29 (0.00 pct) 52502.83 (96.44 pct)
> 512 53082.43 (0.00 pct) 53635.54 (1.04 pct)
> 1024 52940.64 (0.00 pct) 53051.05 (0.20 pct)
>
> NPS Mode - NPS2
> Clients: sched-tip util-avg
> 1 481.84 (0.00 pct) 479.67 (-0.45 pct)
> 2 941.13 (0.00 pct) 927.93 (-1.40 pct)
> 4 1797.61 (0.00 pct) 1770.86 (-1.48 pct)
> 8 3353.37 (0.00 pct) 3360.29 (0.20 pct)
> 16 5779.49 (0.00 pct) 5925.27 (2.52 pct)
> 32 10810.27 (0.00 pct) 10855.17 (0.41 pct)
> 64 17046.83 (0.00 pct) 17457.64 (2.40 pct)
> 128 28799.32 (0.00 pct) 28855.49 (0.19 pct)
> 256 27654.49 (0.00 pct) 47126.18 (70.41 pct)
> 512 51831.52 (0.00 pct) 51219.55 (-1.18 pct)
> 1024 52579.87 (0.00 pct) 50213.68 (-4.50 pct)
>
> NPS Mode - NPS4
> Clients: sched-tip util-avg
> 1 474.08 (0.00 pct) 478.40 (0.91 pct)
> 2 928.23 (0.00 pct) 937.76 (1.02 pct)
> 4 1754.78 (0.00 pct) 1741.17 (-0.77 pct)
> 8 3219.31 (0.00 pct) 3318.00 (3.06 pct)
> 16 5791.53 (0.00 pct) 5687.78 (-1.79 pct)
> 32 9810.76 (0.00 pct) 10866.32 (10.75 pct)
> 64 17098.46 (0.00 pct) 17203.60 (0.61 pct)
> 128 28575.94 (0.00 pct) 28020.97 (-1.94 pct)
> 256 25997.38 (0.00 pct) 47735.83 (83.61 pct)
> 512 47698.94 (0.00 pct) 48220.54 (1.09 pct)
> 1024 51451.30 (0.00 pct) 50455.47 (-1.93 pct)
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Stream with 16 threads.
> built with -DSTREAM_ARRAY_SIZE=128000000, -DNTIMES=10
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> NPS Mode - NPS1
> Test: sched-tip util-avg
> Copy: 175278.66 (0.00 pct) 147847.67 (-15.64 pct)
> Scale: 193235.46 (0.00 pct) 186582.76 (-3.44 pct)
> Add: 220232.14 (0.00 pct) 208519.22 (-5.31 pct)
> Triad: 215526.78 (0.00 pct) 204975.14 (-4.89 pct)
>
> NPS Mode - NPS2
> Test: sched-tip util-avg
> Copy: 166600.09 (0.00 pct) 146456.45 (-12.09 pct)
> Scale: 190820.84 (0.00 pct) 179603.16 (-5.87 pct)
> Add: 214660.01 (0.00 pct) 198636.00 (-7.46 pct)
> Triad: 210879.10 (0.00 pct) 196132.74 (-6.99 pct)
>
> NPS Mode - NPS4
> Test: sched-tip util-avg
> Copy: 173888.83 (0.00 pct) 180948.16 (4.05 pct)
> Scale: 193027.03 (0.00 pct) 199330.65 (3.26 pct)
> Add: 218731.48 (0.00 pct) 221743.63 (1.37 pct)
> Triad: 214651.06 (0.00 pct) 218036.35 (1.57 pct)
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Stream with 16 threads.
> built with -DSTREAM_ARRAY_SIZE=128000000, -DNTIMES=100
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> NPS Mode - NPS1
> Test: sched-tip util-avg
> Copy: 222954.79 (0.00 pct) 219066.70 (-1.74 pct)
> Scale: 208255.97 (0.00 pct) 215060.20 (3.26 pct)
> Add: 247694.16 (0.00 pct) 262893.33 (6.13 pct)
> Triad: 236060.27 (0.00 pct) 250188.38 (5.98 pct)
>
> NPS Mode - NPS2
> Test: sched-tip util-avg
> Copy: 226147.92 (0.00 pct) 228438.70 (1.01 pct)
> Scale: 214059.09 (0.00 pct) 215959.36 (0.88 pct)
> Add: 264978.05 (0.00 pct) 270058.63 (1.91 pct)
> Triad: 253095.73 (0.00 pct) 257466.31 (1.72 pct)
>
> NPS Mode - NPS4
> Test: sched-tip util-avg
> Copy: 223484.37 (0.00 pct) 266929.80 (19.44 pct)
> Scale: 224198.90 (0.00 pct) 235316.80 (4.95 pct)
> Add: 272008.98 (0.00 pct) 294452.15 (8.25 pct)
> Triad: 258219.64 (0.00 pct) 285935.30 (10.73 pct)
> --
>
> We see great results in case of tbench with 256 workers when the
> system is fully loaded which is exactly the kind of scenario this
> patch optimizes for. Hackbench too shows improvements, especially
> in the case of 16-groups.
Thanks for the testing. Currently we have enhanced this patch
according to Peter's suggestion, to make the number of idle cpu
search more gradual. And we have launched some benchmarks to
evaluate the effect. Once it is done, we will send the v2 patch
out and it would be appreciated that you can also help give a glance
at it.
Thanks,
Chenyu
> --
> Thanks and Regards,
> Prateek
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