Re: [PATCH v1] sched/fair: update_pick_idlest() Select group with lowest group_util when idle_cpus are equal
From: Phil Auld
Date: Mon Nov 02 2020 - 09:44:35 EST
Hi,
On Mon, Nov 02, 2020 at 12:06:21PM +0100 Vincent Guittot wrote:
> On Mon, 2 Nov 2020 at 11:50, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Tue, Jul 14, 2020 at 08:59:41AM -0400, peter.puhov@xxxxxxxxxx wrote:
> > > From: Peter Puhov <peter.puhov@xxxxxxxxxx>
> > >
> > > v0: https://lkml.org/lkml/2020/6/16/1286
> > >
> > > Changes in v1:
> > > - Test results formatted in a table form as suggested by Valentin Schneider
> > > - Added explanation by Vincent Guittot why nr_running may not be sufficient
> > >
> > > In slow path, when selecting idlest group, if both groups have type
> > > group_has_spare, only idle_cpus count gets compared.
> > > As a result, if multiple tasks are created in a tight loop,
> > > and go back to sleep immediately
> > > (while waiting for all tasks to be created),
> > > they may be scheduled on the same core, because CPU is back to idle
> > > when the new fork happen.
> > >
> >
> > Intuitively, this made some sense but it's a regression magnet. For those
> > that don't know, I run a grid that among other things, operates similar to
> > the Intel 0-day bot but runs much long-lived tests on a less frequent basis
> > -- can be a few weeks, sometimes longer depending on the grid activity.
> > Where it finds regressions, it bisects them and generates a report.
> >
> > While all tests have not completed, I currently have 14 separate
> > regressions across 4 separate tests on 6 machines which are Broadwell,
> > Haswell and EPYC 2 machines (all x86_64 of course but different generations
> > and vendors). The workload configurations in mmtests are
> >
> > pagealloc-performance-aim9
> > workload-shellscripts
> > workload-kerndevel
> > scheduler-unbound-hackbench
> >
> > When reading the reports, the first and second columns are what it was
> > bisecting against. The second 3rd last commit is the "last good commit"
> > and the last column is "first bad commit". The first bad commit is always
> > this patch
> >
> > The main concern is that all of these workloads have very short-lived tasks
> > which is exactly what this patch is meant to address so either sysbench
> > and futex behave very differently on the machine that was tested or their
> > microbenchmark nature found one good corner case but missed bad ones.
> >
> > I have not investigated why because I do not have the bandwidth
> > to do a detailed study (I was off for a few days and my backlog is
> > severe). However, I recommend in before v5.10 this be reverted and retried.
> > If I'm cc'd on v2, I'll run the same tests through the grid and see what
> > falls out.
>
> I'm going to have a look at the regressions and see if patches that
> have been queued for v5.10 or even more recent patch can help or if
> the patch should be adjusted
>
Fwiw, we have pulled this in, along with some of the 5.10-rc1 fixes in this
area and in the load balancing code.
We found some load balancing improvements and some minor overall perf
gains in a few places, but generally did not see any difference from before
the commit mentioned here.
I'm wondering, Mel, if you have compared 5.10-rc1?
We don't have everything though so it's possible something we have
not pulled back is interacting with this patch, or we are missing something
in our testing, or it's better with the later fixes in 5.10 or ...
something else :)
I'll try to see if we can run some direct 5.8 - 5.9 tests like these.
Cheers,
Phil
> >
> > I'll show one example of each workload from one machine.
> >
> > pagealloc-performance-aim9
> > --------------------------
> >
> > While multiple tests are shown, the exec_test and fork_test are
> > regressing and these are very short lived. 67% regression for exec_test
> > and 32% regression for fork_test
> >
> > initial initial last penup last penup first
> > good-v5.8 bad-v5.9 bad-58934356 bad-e0078e2e good-46132e3a good-aa93cd53 bad-3edecfef
> > Min page_test 522580.00 ( 0.00%) 537880.00 ( 2.93%) 536842.11 ( 2.73%) 542300.00 ( 3.77%) 537993.33 ( 2.95%) 526660.00 ( 0.78%) 532553.33 ( 1.91%)
> > Min brk_test 1987866.67 ( 0.00%) 2028666.67 ( 2.05%) 2016200.00 ( 1.43%) 2014856.76 ( 1.36%) 2004663.56 ( 0.84%) 1984466.67 ( -0.17%) 2025266.67 ( 1.88%)
> > Min exec_test 877.75 ( 0.00%) 284.33 ( -67.61%) 285.14 ( -67.51%) 285.14 ( -67.51%) 852.10 ( -2.92%) 932.05 ( 6.19%) 285.62 ( -67.46%)
> > Min fork_test 3213.33 ( 0.00%) 2154.26 ( -32.96%) 2180.85 ( -32.13%) 2214.10 ( -31.10%) 3257.83 ( 1.38%) 4154.46 ( 29.29%) 2194.15 ( -31.72%)
> > Hmean page_test 544508.39 ( 0.00%) 545446.23 ( 0.17%) 542617.62 ( -0.35%) 546829.87 ( 0.43%) 546439.04 ( 0.35%) 541806.49 ( -0.50%) 546895.25 ( 0.44%)
> > Hmean brk_test 2054683.48 ( 0.00%) 2061982.39 ( 0.36%) 2029765.65 * -1.21%* 2031996.84 * -1.10%* 2040844.18 ( -0.67%) 2009345.37 * -2.21%* 2063861.59 ( 0.45%)
> > Hmean exec_test 896.88 ( 0.00%) 284.71 * -68.26%* 285.65 * -68.15%* 285.45 * -68.17%* 902.85 ( 0.67%) 943.16 * 5.16%* 286.26 * -68.08%*
> > Hmean fork_test 3394.50 ( 0.00%) 2200.37 * -35.18%* 2243.49 * -33.91%* 2244.58 * -33.88%* 3757.31 * 10.69%* 4228.87 * 24.58%* 2237.46 * -34.09%*
> > Stddev page_test 7358.98 ( 0.00%) 3713.10 ( 49.54%) 3177.20 ( 56.83%) 1988.97 ( 72.97%) 5174.09 ( 29.69%) 5755.98 ( 21.78%) 6270.80 ( 14.79%)
> > Stddev brk_test 21505.08 ( 0.00%) 20373.25 ( 5.26%) 9123.25 ( 57.58%) 8935.31 ( 58.45%) 26933.95 ( -25.24%) 11606.00 ( 46.03%) 20779.25 ( 3.38%)
> > Stddev exec_test 13.64 ( 0.00%) 0.36 ( 97.37%) 0.34 ( 97.49%) 0.22 ( 98.38%) 30.95 (-126.92%) 8.43 ( 38.22%) 0.48 ( 96.52%)
> > Stddev fork_test 115.45 ( 0.00%) 37.57 ( 67.46%) 37.22 ( 67.76%) 22.53 ( 80.49%) 274.45 (-137.72%) 32.78 ( 71.61%) 24.24 ( 79.01%)
> > CoeffVar page_test 1.35 ( 0.00%) 0.68 ( 49.62%) 0.59 ( 56.67%) 0.36 ( 73.08%) 0.95 ( 29.93%) 1.06 ( 21.39%) 1.15 ( 15.15%)
> > CoeffVar brk_test 1.05 ( 0.00%) 0.99 ( 5.60%) 0.45 ( 57.05%) 0.44 ( 57.98%) 1.32 ( -26.09%) 0.58 ( 44.81%) 1.01 ( 3.80%)
> > CoeffVar exec_test 1.52 ( 0.00%) 0.13 ( 91.71%) 0.12 ( 92.11%) 0.08 ( 94.92%) 3.42 (-125.23%) 0.89 ( 41.24%) 0.17 ( 89.08%)
> > CoeffVar fork_test 3.40 ( 0.00%) 1.71 ( 49.76%) 1.66 ( 51.19%) 1.00 ( 70.46%) 7.27 (-113.89%) 0.78 ( 77.19%) 1.08 ( 68.12%)
> > Max page_test 553633.33 ( 0.00%) 548986.67 ( -0.84%) 546355.76 ( -1.31%) 549666.67 ( -0.72%) 553746.67 ( 0.02%) 547286.67 ( -1.15%) 558620.00 ( 0.90%)
> > Max brk_test 2068087.94 ( 0.00%) 2081933.33 ( 0.67%) 2044533.33 ( -1.14%) 2045436.38 ( -1.10%) 2074000.00 ( 0.29%) 2027315.12 ( -1.97%) 2081933.33 ( 0.67%)
> > Max exec_test 927.33 ( 0.00%) 285.14 ( -69.25%) 286.28 ( -69.13%) 285.81 ( -69.18%) 951.00 ( 2.55%) 959.33 ( 3.45%) 287.14 ( -69.04%)
> > Max fork_test 3597.60 ( 0.00%) 2267.29 ( -36.98%) 2296.94 ( -36.15%) 2282.10 ( -36.57%) 4054.59 ( 12.70%) 4297.14 ( 19.44%) 2290.28 ( -36.34%)
> > BHmean-50 page_test 547854.63 ( 0.00%) 547923.82 ( 0.01%) 545184.27 ( -0.49%) 548296.84 ( 0.08%) 550707.83 ( 0.52%) 545502.70 ( -0.43%) 550981.79 ( 0.57%)
> > BHmean-50 brk_test 2063783.93 ( 0.00%) 2077311.93 ( 0.66%) 2036886.71 ( -1.30%) 2038740.90 ( -1.21%) 2066350.82 ( 0.12%) 2017773.76 ( -2.23%) 2078929.15 ( 0.73%)
> > BHmean-50 exec_test 906.22 ( 0.00%) 285.04 ( -68.55%) 285.94 ( -68.45%) 285.63 ( -68.48%) 928.41 ( 2.45%) 949.48 ( 4.77%) 286.65 ( -68.37%)
> > BHmean-50 fork_test 3485.94 ( 0.00%) 2230.56 ( -36.01%) 2273.16 ( -34.79%) 2263.22 ( -35.08%) 3973.97 ( 14.00%) 4249.44 ( 21.90%) 2254.13 ( -35.34%)
> > BHmean-95 page_test 546593.48 ( 0.00%) 546144.64 ( -0.08%) 543148.84 ( -0.63%) 547245.43 ( 0.12%) 547220.00 ( 0.11%) 543226.76 ( -0.62%) 548237.46 ( 0.30%)
> > BHmean-95 brk_test 2060981.15 ( 0.00%) 2065065.44 ( 0.20%) 2031007.95 ( -1.45%) 2033569.50 ( -1.33%) 2044198.19 ( -0.81%) 2011638.04 ( -2.39%) 2067443.29 ( 0.31%)
> > BHmean-95 exec_test 898.66 ( 0.00%) 284.74 ( -68.31%) 285.70 ( -68.21%) 285.48 ( -68.23%) 907.76 ( 1.01%) 944.19 ( 5.07%) 286.32 ( -68.14%)
> > BHmean-95 fork_test 3411.98 ( 0.00%) 2204.66 ( -35.38%) 2249.37 ( -34.07%) 2247.40 ( -34.13%) 3810.42 ( 11.68%) 4235.77 ( 24.14%) 2241.48 ( -34.31%)
> > BHmean-99 page_test 546593.48 ( 0.00%) 546144.64 ( -0.08%) 543148.84 ( -0.63%) 547245.43 ( 0.12%) 547220.00 ( 0.11%) 543226.76 ( -0.62%) 548237.46 ( 0.30%)
> > BHmean-99 brk_test 2060981.15 ( 0.00%) 2065065.44 ( 0.20%) 2031007.95 ( -1.45%) 2033569.50 ( -1.33%) 2044198.19 ( -0.81%) 2011638.04 ( -2.39%) 2067443.29 ( 0.31%)
> > BHmean-99 exec_test 898.66 ( 0.00%) 284.74 ( -68.31%) 285.70 ( -68.21%) 285.48 ( -68.23%) 907.76 ( 1.01%) 944.19 ( 5.07%) 286.32 ( -68.14%)
> > BHmean-99 fork_test 3411.98 ( 0.00%) 2204.66 ( -35.38%) 2249.37 ( -34.07%) 2247.40 ( -34.13%) 3810.42 ( 11.68%) 4235.77 ( 24.14%) 2241.48 ( -34.31%)
> >
> > workload-shellscripts
> > ---------------------
> >
> > This is the git test suite. It's mostly sequential that executes lots of
> > small short-lived tasks
> >
> > Comparison
> > ==========
> > initial initial last penup last penup first
> > good-v5.8 bad-v5.9 bad-58934356 bad-e0078e2e good-46132e3a good-aa93cd53 bad-3edecfef
> > Min User 798.92 ( 0.00%) 897.51 ( -12.34%) 894.39 ( -11.95%) 896.18 ( -12.17%) 799.34 ( -0.05%) 796.94 ( 0.25%) 894.75 ( -11.99%)
> > Min System 479.24 ( 0.00%) 603.24 ( -25.87%) 596.36 ( -24.44%) 597.34 ( -24.64%) 484.00 ( -0.99%) 482.64 ( -0.71%) 599.17 ( -25.03%)
> > Min Elapsed 1225.72 ( 0.00%) 1443.47 ( -17.77%) 1434.25 ( -17.01%) 1434.08 ( -17.00%) 1230.97 ( -0.43%) 1226.47 ( -0.06%) 1436.45 ( -17.19%)
> > Min CPU 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%)
> > Amean User 799.84 ( 0.00%) 899.00 * -12.40%* 896.15 * -12.04%* 897.33 * -12.19%* 800.47 ( -0.08%) 797.96 * 0.23%* 896.35 * -12.07%*
> > Amean System 480.68 ( 0.00%) 605.14 * -25.89%* 598.59 * -24.53%* 599.63 * -24.75%* 485.92 * -1.09%* 483.51 * -0.59%* 600.67 * -24.96%*
> > Amean Elapsed 1226.35 ( 0.00%) 1444.06 * -17.75%* 1434.57 * -16.98%* 1436.62 * -17.15%* 1231.60 * -0.43%* 1228.06 ( -0.14%) 1436.65 * -17.15%*
> > Amean CPU 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%)
> > Stddev User 0.79 ( 0.00%) 1.20 ( -51.32%) 1.32 ( -65.89%) 1.07 ( -35.47%) 1.12 ( -40.77%) 1.08 ( -36.32%) 1.38 ( -73.53%)
> > Stddev System 0.90 ( 0.00%) 1.26 ( -40.06%) 1.73 ( -91.63%) 1.50 ( -66.48%) 1.08 ( -20.06%) 0.74 ( 17.38%) 1.04 ( -15.98%)
> > Stddev Elapsed 0.44 ( 0.00%) 0.53 ( -18.89%) 0.28 ( 36.46%) 1.77 (-298.99%) 0.53 ( -19.49%) 2.02 (-356.27%) 0.24 ( 46.45%)
> > Stddev CPU 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> > CoeffVar User 0.10 ( 0.00%) 0.13 ( -34.63%) 0.15 ( -48.07%) 0.12 ( -20.75%) 0.14 ( -40.66%) 0.14 ( -36.64%) 0.15 ( -54.85%)
> > CoeffVar System 0.19 ( 0.00%) 0.21 ( -11.26%) 0.29 ( -53.88%) 0.25 ( -33.45%) 0.22 ( -18.76%) 0.15 ( 17.86%) 0.17 ( 7.19%)
> > CoeffVar Elapsed 0.04 ( 0.00%) 0.04 ( -0.96%) 0.02 ( 45.68%) 0.12 (-240.59%) 0.04 ( -18.98%) 0.16 (-355.64%) 0.02 ( 54.29%)
> > CoeffVar CPU 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> > Max User 801.05 ( 0.00%) 900.27 ( -12.39%) 897.95 ( -12.10%) 899.06 ( -12.24%) 802.29 ( -0.15%) 799.47 ( 0.20%) 898.39 ( -12.15%)
> > Max System 481.60 ( 0.00%) 606.40 ( -25.91%) 600.94 ( -24.78%) 601.51 ( -24.90%) 486.59 ( -1.04%) 484.23 ( -0.55%) 602.04 ( -25.01%)
> > Max Elapsed 1226.94 ( 0.00%) 1444.85 ( -17.76%) 1434.89 ( -16.95%) 1438.52 ( -17.24%) 1232.42 ( -0.45%) 1231.52 ( -0.37%) 1437.04 ( -17.12%)
> > Max CPU 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%)
> > BAmean-50 User 799.16 ( 0.00%) 897.73 ( -12.33%) 895.06 ( -12.00%) 896.51 ( -12.18%) 799.68 ( -0.07%) 797.09 ( 0.26%) 895.20 ( -12.02%)
> > BAmean-50 System 479.89 ( 0.00%) 603.93 ( -25.85%) 597.00 ( -24.40%) 598.39 ( -24.69%) 485.10 ( -1.09%) 482.75 ( -0.60%) 599.83 ( -24.99%)
> > BAmean-50 Elapsed 1225.99 ( 0.00%) 1443.59 ( -17.75%) 1434.34 ( -16.99%) 1434.97 ( -17.05%) 1231.20 ( -0.42%) 1226.66 ( -0.05%) 1436.47 ( -17.17%)
> > BAmean-50 CPU 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%)
> > BAmean-95 User 799.53 ( 0.00%) 898.68 ( -12.40%) 895.69 ( -12.03%) 896.90 ( -12.18%) 800.01 ( -0.06%) 797.58 ( 0.24%) 895.85 ( -12.05%)
> > BAmean-95 System 480.45 ( 0.00%) 604.82 ( -25.89%) 598.01 ( -24.47%) 599.16 ( -24.71%) 485.75 ( -1.10%) 483.33 ( -0.60%) 600.33 ( -24.95%)
> > BAmean-95 Elapsed 1226.21 ( 0.00%) 1443.86 ( -17.75%) 1434.49 ( -16.99%) 1436.15 ( -17.12%) 1231.40 ( -0.42%) 1227.20 ( -0.08%) 1436.55 ( -17.15%)
> > BAmean-95 CPU 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%)
> > BAmean-99 User 799.53 ( 0.00%) 898.68 ( -12.40%) 895.69 ( -12.03%) 896.90 ( -12.18%) 800.01 ( -0.06%) 797.58 ( 0.24%) 895.85 ( -12.05%)
> > BAmean-99 System 480.45 ( 0.00%) 604.82 ( -25.89%) 598.01 ( -24.47%) 599.16 ( -24.71%) 485.75 ( -1.10%) 483.33 ( -0.60%) 600.33 ( -24.95%)
> > BAmean-99 Elapsed 1226.21 ( 0.00%) 1443.86 ( -17.75%) 1434.49 ( -16.99%) 1436.15 ( -17.12%) 1231.40 ( -0.42%) 1227.20 ( -0.08%) 1436.55 ( -17.15%)
> > BAmean-99 CPU 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%) 104.00 ( 0.00%)
> >
> > This is showing a 17% regression in the time to complete the test
> >
> > workload-kerndevel
> > ------------------
> >
> > This is a kernel building benchmark varying the number of subjobs with
> > -J
> >
> > initial initial last penup last penup first
> > good-v5.8 bad-v5.9 bad-58934356 bad-e0078e2e good-46132e3a good-aa93cd53 bad-3edecfef
> > Amean syst-2 138.51 ( 0.00%) 169.35 * -22.26%* 170.13 * -22.83%* 169.12 * -22.09%* 136.47 * 1.47%* 137.73 ( 0.57%) 169.24 * -22.18%*
> > Amean elsp-2 489.41 ( 0.00%) 542.92 * -10.93%* 548.96 * -12.17%* 544.82 * -11.32%* 485.33 * 0.83%* 487.26 ( 0.44%) 542.35 * -10.82%*
> > Amean syst-4 148.11 ( 0.00%) 171.27 * -15.63%* 171.14 * -15.55%* 170.82 * -15.33%* 146.13 * 1.34%* 146.38 * 1.17%* 170.52 * -15.13%*
> > Amean elsp-4 266.90 ( 0.00%) 285.40 * -6.93%* 286.50 * -7.34%* 285.14 * -6.83%* 263.71 * 1.20%* 264.76 * 0.80%* 285.88 * -7.11%*
> > Amean syst-8 158.64 ( 0.00%) 167.19 * -5.39%* 166.95 * -5.24%* 165.54 * -4.35%* 157.12 * 0.96%* 157.69 * 0.60%* 166.78 * -5.13%*
> > Amean elsp-8 148.42 ( 0.00%) 151.32 * -1.95%* 154.00 * -3.76%* 151.64 * -2.17%* 147.79 ( 0.42%) 148.90 ( -0.32%) 152.56 * -2.79%*
> > Amean syst-16 165.21 ( 0.00%) 166.41 * -0.73%* 166.96 * -1.06%* 166.17 ( -0.58%) 164.32 * 0.54%* 164.05 * 0.70%* 165.80 ( -0.36%)
> > Amean elsp-16 83.17 ( 0.00%) 83.23 ( -0.07%) 83.75 ( -0.69%) 83.48 ( -0.37%) 83.08 ( 0.12%) 83.07 ( 0.12%) 83.27 ( -0.12%)
> > Amean syst-32 164.42 ( 0.00%) 164.43 ( -0.00%) 164.43 ( -0.00%) 163.40 * 0.62%* 163.38 * 0.63%* 163.18 * 0.76%* 163.70 * 0.44%*
> > Amean elsp-32 47.81 ( 0.00%) 48.83 * -2.14%* 48.64 * -1.73%* 48.46 ( -1.36%) 48.28 ( -0.97%) 48.16 ( -0.74%) 48.15 ( -0.71%)
> > Amean syst-64 189.79 ( 0.00%) 192.63 * -1.50%* 191.19 * -0.74%* 190.86 * -0.56%* 189.08 ( 0.38%) 188.52 * 0.67%* 190.52 ( -0.39%)
> > Amean elsp-64 35.49 ( 0.00%) 35.89 ( -1.13%) 36.39 * -2.51%* 35.93 ( -1.23%) 34.69 * 2.28%* 35.52 ( -0.06%) 35.60 ( -0.30%)
> > Amean syst-128 200.15 ( 0.00%) 202.72 * -1.28%* 202.34 * -1.09%* 200.98 * -0.41%* 200.56 ( -0.20%) 198.12 * 1.02%* 201.01 * -0.43%*
> > Amean elsp-128 34.34 ( 0.00%) 34.99 * -1.89%* 34.92 * -1.68%* 34.90 * -1.61%* 34.51 * -0.50%* 34.37 ( -0.08%) 35.02 * -1.98%*
> > Amean syst-160 197.14 ( 0.00%) 199.39 * -1.14%* 198.76 * -0.82%* 197.71 ( -0.29%) 196.62 ( 0.26%) 195.55 * 0.81%* 197.06 ( 0.04%)
> > Amean elsp-160 34.51 ( 0.00%) 35.15 * -1.87%* 35.14 * -1.83%* 35.06 * -1.61%* 34.29 * 0.63%* 34.43 ( 0.23%) 35.10 * -1.73%*
> >
> > This is showing a 10.93% regression in elapsed time with just two jobs
> > (elsp-2). The regression goes away when there are a number of jobs so
> > it's short-lived tasks on a mostly idle machine that is a problem
> > Interestingly, it shows a lot of additional system CPU usage time
> > (syst-2) so it's probable that the issue can be inferred from perf with
> > a perf diff to show where all the extra time is being lost.
> >
> > While I say workload-kerndevel, I actually was using a modified version of
> > the configuration that tested ext4 and xfs on test partitions. Both show
> > regressions so this is not filesystem-specific (without the modification,
> > the base filesystem would be btrfs on my test grid which some would find
> > less interesting)
> >
> > scheduler-unbound-hackbench
> > ---------------------------
> >
> > I don't think hackbench needs an introduction. It's varying the number
> > of groups but as each group has lots of tasks, the machine is heavily
> > loaded.
> >
> > initial initial last penup last penup first
> > good-v5.8 bad-22fbc037cd32 bad-58934356 bad-e0078e2e good-46132e3a good-aa93cd53 bad-3edecfef
> > Min 1 0.6470 ( 0.00%) 0.5200 ( 19.63%) 0.6730 ( -4.02%) 0.5230 ( 19.17%) 0.6620 ( -2.32%) 0.6740 ( -4.17%) 0.6170 ( 4.64%)
> > Min 4 0.7510 ( 0.00%) 0.7460 ( 0.67%) 0.7230 ( 3.73%) 0.7450 ( 0.80%) 0.7540 ( -0.40%) 0.7490 ( 0.27%) 0.7520 ( -0.13%)
> > Min 7 0.8140 ( 0.00%) 0.8300 ( -1.97%) 0.7880 ( 3.19%) 0.7880 ( 3.19%) 0.7870 ( 3.32%) 0.8170 ( -0.37%) 0.7990 ( 1.84%)
> > Min 12 0.9500 ( 0.00%) 0.9140 ( 3.79%) 0.9070 ( 4.53%) 0.9200 ( 3.16%) 0.9290 ( 2.21%) 0.9180 ( 3.37%) 0.9070 ( 4.53%)
> > Min 21 1.2210 ( 0.00%) 1.1560 ( 5.32%) 1.1230 ( 8.03%) 1.1480 ( 5.98%) 1.2730 ( -4.26%) 1.2010 ( 1.64%) 1.1610 ( 4.91%)
> > Min 30 1.6500 ( 0.00%) 1.5960 ( 3.27%) 1.5010 ( 9.03%) 1.5620 ( 5.33%) 1.6130 ( 2.24%) 1.5920 ( 3.52%) 1.5540 ( 5.82%)
> > Min 48 2.2550 ( 0.00%) 2.2610 ( -0.27%) 2.2040 ( 2.26%) 2.1940 ( 2.71%) 2.1090 ( 6.47%) 2.0910 ( 7.27%) 2.1300 ( 5.54%)
> > Min 79 2.9090 ( 0.00%) 3.3210 ( -14.16%) 3.2140 ( -10.48%) 3.1310 ( -7.63%) 2.8970 ( 0.41%) 3.0400 ( -4.50%) 3.2590 ( -12.03%)
> > Min 110 3.5080 ( 0.00%) 4.2600 ( -21.44%) 4.0060 ( -14.20%) 4.1110 ( -17.19%) 3.6680 ( -4.56%) 3.5370 ( -0.83%) 4.0550 ( -15.59%)
> > Min 141 4.1840 ( 0.00%) 4.8090 ( -14.94%) 4.9600 ( -18.55%) 4.7310 ( -13.07%) 4.3650 ( -4.33%) 4.2590 ( -1.79%) 4.8320 ( -15.49%)
> > Min 172 5.2690 ( 0.00%) 5.6350 ( -6.95%) 5.6140 ( -6.55%) 5.5550 ( -5.43%) 5.0390 ( 4.37%) 5.0940 ( 3.32%) 5.8190 ( -10.44%)
> > Amean 1 0.6867 ( 0.00%) 0.6470 ( 5.78%) 0.6830 ( 0.53%) 0.5993 ( 12.72%) 0.6857 ( 0.15%) 0.6897 ( -0.44%) 0.6600 ( 3.88%)
> > Amean 4 0.7603 ( 0.00%) 0.7477 ( 1.67%) 0.7413 ( 2.50%) 0.7517 ( 1.14%) 0.7667 ( -0.83%) 0.7557 ( 0.61%) 0.7583 ( 0.26%)
> > Amean 7 0.8377 ( 0.00%) 0.8347 ( 0.36%) 0.8333 ( 0.52%) 0.7997 * 4.54%* 0.8160 ( 2.59%) 0.8323 ( 0.64%) 0.8183 ( 2.31%)
> > Amean 12 0.9653 ( 0.00%) 0.9390 ( 2.73%) 0.9173 * 4.97%* 0.9357 ( 3.07%) 0.9460 ( 2.00%) 0.9383 ( 2.80%) 0.9230 * 4.39%*
> > Amean 21 1.2400 ( 0.00%) 1.2260 ( 1.13%) 1.1733 ( 5.38%) 1.1833 * 4.57%* 1.2893 * -3.98%* 1.2620 ( -1.77%) 1.2043 ( 2.88%)
> > Amean 30 1.6743 ( 0.00%) 1.6393 ( 2.09%) 1.5530 * 7.25%* 1.6070 ( 4.02%) 1.6293 ( 2.69%) 1.6167 * 3.44%* 1.6280 ( 2.77%)
> > Amean 48 2.2760 ( 0.00%) 2.2987 ( -1.00%) 2.2257 * 2.21%* 2.2423 ( 1.48%) 2.1843 * 4.03%* 2.1687 * 4.72%* 2.1890 * 3.82%*
> > Amean 79 3.0977 ( 0.00%) 3.3847 * -9.27%* 3.2540 ( -5.05%) 3.2367 ( -4.49%) 3.0067 ( 2.94%) 3.1263 ( -0.93%) 3.2983 ( -6.48%)
> > Amean 110 3.6460 ( 0.00%) 4.3140 * -18.32%* 4.1720 * -14.43%* 4.1980 * -15.14%* 3.7230 ( -2.11%) 3.6990 ( -1.45%) 4.1790 * -14.62%*
> > Amean 141 4.2420 ( 0.00%) 4.9697 * -17.15%* 4.9973 * -17.81%* 4.8940 * -15.37%* 4.4057 * -3.86%* 4.3493 ( -2.53%) 4.9610 * -16.95%*
> > Amean 172 5.2830 ( 0.00%) 5.8717 * -11.14%* 5.7370 * -8.59%* 5.8280 * -10.32%* 5.0943 * 3.57%* 5.1083 * 3.31%* 5.9720 * -13.04%*
> >
> > This is showing 12% regression for 79 groups. This one is interesting
> > because EPYC2 seems to be the one that is most affected by this. EPYC2
> > has a different topology that a similar X86 machine in that it has
> > multiple last-level caches so the sched domain groups it looks at are
> > smaller than happens on other machines.
> >
> > Given the number of machines and workloads affected, can we revert and
> > retry? I have not tested against current mainline as scheduler details
> > have changed again but I can do so if desired.
> >
> > --
> > Mel Gorman
> > SUSE Labs
>
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