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  1. 25 Sep, 2020 11 commits
    • Barry Song's avatar
      sched/fair: Use dst group while checking imbalance for NUMA balancer · 233e7aca
      Barry Song authored 
      Barry Song noted the following

	Something is wrong. In find_busiest_group(), we are checking if
	src has higher load, however, in task_numa_find_cpu(), we are
	checking if dst will have higher load after balancing. It seems
	it is not sensible to check src.

	It maybe cause wrong imbalance value, for example,

	if dst_running = env->dst_stats.nr_running + 1 results in 3 or
	above, and src_running = env->src_stats.nr_running - 1 results
	in 1;

	The current code is thinking imbalance as 0 since src_running is
	smaller than 2.  This is inconsistent with load balancer.

Basically, in find_busiest_group(), the NUMA imbalance is ignored if moving
a task "from an almost idle domain" to a "domain with spare capacity". This
patch forbids movement "from a misplaced domain" to "an almost idle domain"
as that is closer to what the CPU load balancer expects.

This patch is not a universal win. The old behaviour was intended to allow
a task from an almost idle NUMA node to migrate to its preferred node if
the destination had capacity but there are corner cases.  For example,
a NAS compute load could be parallelised to use 1/3rd of available CPUs
but not all those potential tasks are active at all times allowing this
logic to trigger. An obvious example is specjbb 2005 running various
numbers of warehouses on a 2 socket box with 80 cpus.

specjbb
                               5.9.0-rc4              5.9.0-rc4
                                 vanilla        dstbalance-v1r1
Hmean     tput-1     46425.00 (   0.00%)    43394.00 *  -6.53%*
Hmean     tput-2     98416.00 (   0.00%)    96031.00 *  -2.42%*
Hmean     tput-3    150184.00 (   0.00%)   148783.00 *  -0.93%*
Hmean     tput-4    200683.00 (   0.00%)   197906.00 *  -1.38%*
Hmean     tput-5    236305.00 (   0.00%)   245549.00 *   3.91%*
Hmean     tput-6    281559.00 (   0.00%)   285692.00 *   1.47%*
Hmean     tput-7    338558.00 (   0.00%)   334467.00 *  -1.21%*
Hmean     tput-8    340745.00 (   0.00%)   372501.00 *   9.32%*
Hmean     tput-9    424343.00 (   0.00%)   413006.00 *  -2.67%*
Hmean     tput-10   421854.00 (   0.00%)   434261.00 *   2.94%*
Hmean     tput-11   493256.00 (   0.00%)   485330.00 *  -1.61%*
Hmean     tput-12   549573.00 (   0.00%)   529959.00 *  -3.57%*
Hmean     tput-13   593183.00 (   0.00%)   555010.00 *  -6.44%*
Hmean     tput-14   588252.00 (   0.00%)   599166.00 *   1.86%*
Hmean     tput-15   623065.00 (   0.00%)   642713.00 *   3.15%*
Hmean     tput-16   703924.00 (   0.00%)   660758.00 *  -6.13%*
Hmean     tput-17   666023.00 (   0.00%)   697675.00 *   4.75%*
Hmean     tput-18   761502.00 (   0.00%)   758360.00 *  -0.41%*
Hmean     tput-19   796088.00 (   0.00%)   798368.00 *   0.29%*
Hmean     tput-20   733564.00 (   0.00%)   823086.00 *  12.20%*
Hmean     tput-21   840980.00 (   0.00%)   856711.00 *   1.87%*
Hmean     tput-22   804285.00 (   0.00%)   872238.00 *   8.45%*
Hmean     tput-23   795208.00 (   0.00%)   889374.00 *  11.84%*
Hmean     tput-24   848619.00 (   0.00%)   966783.00 *  13.92%*
Hmean     tput-25   750848.00 (   0.00%)   903790.00 *  20.37%*
Hmean     tput-26   780523.00 (   0.00%)   962254.00 *  23.28%*
Hmean     tput-27  1042245.00 (   0.00%)   991544.00 *  -4.86%*
Hmean     tput-28  1090580.00 (   0.00%)  1035926.00 *  -5.01%*
Hmean     tput-29   999483.00 (   0.00%)  1082948.00 *   8.35%*
Hmean     tput-30  1098663.00 (   0.00%)  1113427.00 *   1.34%*
Hmean     tput-31  1125671.00 (   0.00%)  1134175.00 *   0.76%*
Hmean     tput-32   968167.00 (   0.00%)  1250286.00 *  29.14%*
Hmean     tput-33  1077676.00 (   0.00%)  1060893.00 *  -1.56%*
Hmean     tput-34  1090538.00 (   0.00%)  1090933.00 *   0.04%*
Hmean     tput-35   967058.00 (   0.00%)  1107421.00 *  14.51%*
Hmean     tput-36  1051745.00 (   0.00%)  1210663.00 *  15.11%*
Hmean     tput-37  1019465.00 (   0.00%)  1351446.00 *  32.56%*
Hmean     tput-38  1083102.00 (   0.00%)  1064541.00 *  -1.71%*
Hmean     tput-39  1232990.00 (   0.00%)  1303623.00 *   5.73%*
Hmean     tput-40  1175542.00 (   0.00%)  1340943.00 *  14.07%*
Hmean     tput-41  1127826.00 (   0.00%)  1339492.00 *  18.77%*
Hmean     tput-42  1198313.00 (   0.00%)  1411023.00 *  17.75%*
Hmean     tput-43  1163733.00 (   0.00%)  1228253.00 *   5.54%*
Hmean     tput-44  1305562.00 (   0.00%)  1357886.00 *   4.01%*
Hmean     tput-45  1326752.00 (   0.00%)  1406061.00 *   5.98%*
Hmean     tput-46  1339424.00 (   0.00%)  1418451.00 *   5.90%*
Hmean     tput-47  1415057.00 (   0.00%)  1381570.00 *  -2.37%*
Hmean     tput-48  1392003.00 (   0.00%)  1421167.00 *   2.10%*
Hmean     tput-49  1408374.00 (   0.00%)  1418659.00 *   0.73%*
Hmean     tput-50  1359822.00 (   0.00%)  1391070.00 *   2.30%*
Hmean     tput-51  1414246.00 (   0.00%)  1392679.00 *  -1.52%*
Hmean     tput-52  1432352.00 (   0.00%)  1354020.00 *  -5.47%*
Hmean     tput-53  1387563.00 (   0.00%)  1409563.00 *   1.59%*
Hmean     tput-54  1406420.00 (   0.00%)  1388711.00 *  -1.26%*
Hmean     tput-55  1438804.00 (   0.00%)  1387472.00 *  -3.57%*
Hmean     tput-56  1399465.00 (   0.00%)  1400296.00 *   0.06%*
Hmean     tput-57  1428132.00 (   0.00%)  1396399.00 *  -2.22%*
Hmean     tput-58  1432385.00 (   0.00%)  1386253.00 *  -3.22%*
Hmean     tput-59  1421612.00 (   0.00%)  1371416.00 *  -3.53%*
Hmean     tput-60  1429423.00 (   0.00%)  1389412.00 *  -2.80%*
Hmean     tput-61  1396230.00 (   0.00%)  1351122.00 *  -3.23%*
Hmean     tput-62  1418396.00 (   0.00%)  1383098.00 *  -2.49%*
Hmean     tput-63  1409918.00 (   0.00%)  1374662.00 *  -2.50%*
Hmean     tput-64  1410236.00 (   0.00%)  1376216.00 *  -2.41%*
Hmean     tput-65  1396405.00 (   0.00%)  1364418.00 *  -2.29%*
Hmean     tput-66  1395975.00 (   0.00%)  1357326.00 *  -2.77%*
Hmean     tput-67  1392986.00 (   0.00%)  1349642.00 *  -3.11%*
Hmean     tput-68  1386541.00 (   0.00%)  1343261.00 *  -3.12%*
Hmean     tput-69  1374407.00 (   0.00%)  1342588.00 *  -2.32%*
Hmean     tput-70  1377513.00 (   0.00%)  1334654.00 *  -3.11%*
Hmean     tput-71  1369319.00 (   0.00%)  1334952.00 *  -2.51%*
Hmean     tput-72  1354635.00 (   0.00%)  1329005.00 *  -1.89%*
Hmean     tput-73  1350933.00 (   0.00%)  1318942.00 *  -2.37%*
Hmean     tput-74  1351714.00 (   0.00%)  1316347.00 *  -2.62%*
Hmean     tput-75  1352198.00 (   0.00%)  1309974.00 *  -3.12%*
Hmean     tput-76  1349490.00 (   0.00%)  1286064.00 *  -4.70%*
Hmean     tput-77  1336131.00 (   0.00%)  1303684.00 *  -2.43%*
Hmean     tput-78  1308896.00 (   0.00%)  1271024.00 *  -2.89%*
Hmean     tput-79  1326703.00 (   0.00%)  1290862.00 *  -2.70%*
Hmean     tput-80  1336199.00 (   0.00%)  1291629.00 *  -3.34%*

The performance at the mid-point is better but not universally better. The
patch is a mixed bag depending on the workload, machine and overall
levels of utilisation. Sometimes it's better (sometimes much better),
other times it is worse (sometimes much worse). Given that there isn't a
universally good decision in this section and more people seem to prefer
the patch then it may be best to keep the LB decisions consistent and
revisit imbalance handling when the load balancer code changes settle down.

Jirka Hladky added the following observation.

	Our results are mostly in line with what you see. We observe
	big gains (20-50%) when the system is loaded to 1/3 of the
	maximum capacity and mixed results at the full load - some
	workloads benefit from the patch at the full load, others not,
	but performance changes at the full load are mostly within the
	noise of results (+/-5%). Overall, we think this patch is helpful.

[mgorman@techsingularity.net: Rewrote changelog]
Fixes: fb86f5b2 ("sched/numa: Use similar logic to the load balancer for moving between domains with spare capacity")
Signed-off-by: default avatarBarry Song <song.bao.hua@hisilicon.com>
Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200921221849.GI3179@techsingularity.net
      233e7aca
    • Vincent Guittot's avatar
      sched/fair: Reduce busy load balance interval · 6e749913
      Vincent Guittot authored 
      The busy_factor, which increases load balance interval when a cpu is busy,
is set to 32 by default. This value generates some huge LB interval on
large system like the THX2 made of 2 node x 28 cores x 4 threads.
For such system, the interval increases from 112ms to 3584ms at MC level.
And from 228ms to 7168ms at NUMA level.

Even on smaller system, a lower busy factor has shown improvement on the
fair distribution of the running time so let reduce it for all.
Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarPhil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/20200921072424.14813-5-vincent.guittot@linaro.org
      6e749913
    • Vincent Guittot's avatar
      sched/fair: Minimize concurrent LBs between domain level · e4d32e4d
      Vincent Guittot authored 
      sched domains tend to trigger simultaneously the load balance loop but
the larger domains often need more time to collect statistics. This
slowness makes the larger domain trying to detach tasks from a rq whereas
tasks already migrated somewhere else at a sub-domain level. This is not
a real problem for idle LB because the period of smaller domains will
increase with its CPUs being busy and this will let time for higher ones
to pulled tasks. But this becomes a problem when all CPUs are already busy
because all domains stay synced when they trigger their LB.

A simple way to minimize simultaneous LB of all domains is to decrement the
the busy interval by 1 jiffies. Because of the busy_factor, the interval of
larger domain will not be a multiple of smaller ones anymore.
Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarPhil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/20200921072424.14813-4-vincent.guittot@linaro.org
      e4d32e4d
    • Vincent Guittot's avatar
      sched/fair: Reduce minimal imbalance threshold · 2208cdaa
      Vincent Guittot authored 
      The 25% default imbalance threshold for DIE and NUMA domain is large
enough to generate significant unfairness between threads. A typical
example is the case of 11 threads running on 2x4 CPUs. The imbalance of
20% between the 2 groups of 4 cores is just low enough to not trigger
the load balance between the 2 groups. We will have always the same 6
threads on one group of 4 CPUs and the other 5 threads on the other
group of CPUS. With a fair time sharing in each group, we ends up with
+20% running time for the group of 5 threads.

Consider decreasing the imbalance threshold for overloaded case where we
use the load to balance task and to ensure fair time sharing.
Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarPhil Auld <pauld@redhat.com>
Acked-by: default avatarHillf Danton <hdanton@sina.com>
Link: https://lkml.kernel.org/r/20200921072424.14813-3-vincent.guittot@linaro.org
      2208cdaa
    • Vincent Guittot's avatar
      sched/fair: Relax constraint on task's load during load balance · 5a7f5559
      Vincent Guittot authored 
      Some UCs like 9 always running tasks on 8 CPUs can't be balanced and the
load balancer currently migrates the waiting task between the CPUs in an
almost random manner. The success of a rq pulling a task depends of the
value of nr_balance_failed of its domains and its ability to be faster
than others to detach it. This behavior results in an unfair distribution
of the running time between tasks because some CPUs will run most of the
time, if not always, the same task whereas others will share their time
between several tasks.

Instead of using nr_balance_failed as a boolean to relax the condition
for detaching task, the LB will use nr_balanced_failed to relax the
threshold between the tasks'load and the imbalance. This mecanism
prevents the same rq or domain to always win the load balance fight.
Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarPhil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/20200921072424.14813-2-vincent.guittot@linaro.org
      5a7f5559
    • Xianting Tian's avatar
      sched/fair: Remove the force parameter of update_tg_load_avg() · fe749158
      Xianting Tian authored 
      In the file fair.c, sometims update_tg_load_avg(cfs_rq, 0) is used,
sometimes update_tg_load_avg(cfs_rq, false) is used.
update_tg_load_avg() has the parameter force, but in current code,
it never set 1 or true to it, so remove the force parameter.
Signed-off-by: default avatarXianting Tian <tian.xianting@h3c.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200924014755.36253-1-tian.xianting@h3c.com
      fe749158
    • Xunlei Pang's avatar
      sched/fair: Fix wrong cpu selecting from isolated domain · df3cb4ea
      Xunlei Pang authored 
      We've met problems that occasionally tasks with full cpumask
(e.g. by putting it into a cpuset or setting to full affinity)
were migrated to our isolated cpus in production environment.

After some analysis, we found that it is due to the current
select_idle_smt() not considering the sched_domain mask.

Steps to reproduce on my 31-CPU hyperthreads machine:
1. with boot parameter: "isolcpus=domain,2-31"
   (thread lists: 0,16 and 1,17)
2. cgcreate -g cpu:test; cgexec -g cpu:test "test_threads"
3. some threads will be migrated to the isolated cpu16~17.

Fix it by checking the valid domain mask in select_idle_smt().

Fixes: 10e2f1ac ("sched/core: Rewrite and improve select_idle_siblings())
Reported-by: default avatarWetp Zhang <wetp.zy@linux.alibaba.com>
Signed-off-by: default avatarXunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarJiang Biao <benbjiang@tencent.com>
Reviewed-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/1600930127-76857-1-git-send-email-xlpang@linux.alibaba.com
      df3cb4ea
    • YueHaibing's avatar
      sched: Remove unused inline function uclamp_bucket_base_value() · 51bd5121
      YueHaibing authored 
      There is no caller in tree, so can remove it.
Signed-off-by: default avatarYueHaibing <yuehaibing@huawei.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lkml.kernel.org/r/20200922132410.48440-1-yuehaibing@huawei.com
      51bd5121
    • Daniel Bristot de Oliveira's avatar
      sched/rt: Disable RT_RUNTIME_SHARE by default · 2586af1a
      Daniel Bristot de Oliveira authored 
      The RT_RUNTIME_SHARE sched feature enables the sharing of rt_runtime
between CPUs, allowing a CPU to run a real-time task up to 100% of the
time while leaving more space for non-real-time tasks to run on the CPU
that lend rt_runtime.

The problem is that a CPU can easily borrow enough rt_runtime to allow
a spinning rt-task to run forever, starving per-cpu tasks like kworkers,
which are non-real-time by design.

This patch disables RT_RUNTIME_SHARE by default, avoiding this problem.
The feature will still be present for users that want to enable it,
though.
Signed-off-by: default avatarDaniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarWei Wang <wvw@google.com>
Link: https://lkml.kernel.org/r/b776ab46817e3db5d8ef79175fa0d71073c051c7.1600697903.git.bristot@redhat.com
      2586af1a
    • Lucas Stach's avatar
      sched/deadline: Fix stale throttling on de-/boosted tasks · 46fcc4b0
      Lucas Stach authored 
      When a boosted task gets throttled, what normally happens is that it's
immediately enqueued again with ENQUEUE_REPLENISH, which replenishes the
runtime and clears the dl_throttled flag. There is a special case however:
if the throttling happened on sched-out and the task has been deboosted in
the meantime, the replenish is skipped as the task will return to its
normal scheduling class. This leaves the task with the dl_throttled flag
set.

Now if the task gets boosted up to the deadline scheduling class again
while it is sleeping, it's still in the throttled state. The normal wakeup
however will enqueue the task with ENQUEUE_REPLENISH not set, so we don't
actually place it on the rq. Thus we end up with a task that is runnable,
but not actually on the rq and neither a immediate replenishment happens,
nor is the replenishment timer set up, so the task is stuck in
forever-throttled limbo.

Clear the dl_throttled flag before dropping back to the normal scheduling
class to fix this issue.
Signed-off-by: default avatarLucas Stach <l.stach@pengutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200831110719.2126930-1-l.stach@pengutronix.de
      46fcc4b0
    • Vincent Guittot's avatar
      sched/numa: Use runnable_avg to classify node · 8e0e0eda
      Vincent Guittot authored 
      Use runnable_avg to classify numa node state similarly to what is done for
normal load balancer. This helps to ensure that numa and normal balancers
use the same view of the state of the system.

Large arm64system: 2 nodes / 224 CPUs:

  hackbench -l (256000/#grp) -g #grp

  grp    tip/sched/core         +patchset              improvement
  1      14,008(+/- 4,99 %)     13,800(+/- 3.88 %)     1,48 %
  4       4,340(+/- 5.35 %)      4.283(+/- 4.85 %)     1,33 %
  16      3,357(+/- 0.55 %)      3.359(+/- 0.54 %)    -0,06 %
  32      3,050(+/- 0.94 %)      3.039(+/- 1,06 %)     0,38 %
  64      2.968(+/- 1,85 %)      3.006(+/- 2.92 %)    -1.27 %
  128     3,290(+/-12.61 %)      3,108(+/- 5.97 %)     5.51 %
  256     3.235(+/- 3.95 %)      3,188(+/- 2.83 %)     1.45 %
Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMel Gorman <mgorman@suse.de>
Link: https://lkml.kernel.org/r/20200921072959.16317-1-vincent.guittot@linaro.org
      8e0e0eda
  3. 09 Sep, 2020 1 commit
  5. 04 Sep, 2020 1 commit
  7. 26 Aug, 2020 7 commits
  9. 19 Aug, 2020 16 commits
  11. 18 Aug, 2020 4 commits
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