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SubjectRe: [PATCH v2 04/19] sched/numa: Set preferred_node based on best_cpu
On Wed, Jun 20, 2018 at 10:32:45PM +0530, Srikar Dronamraju wrote:
> Currently preferred node is set to dst_nid which is the last node in the
> iteration whose group weight or task weight is greater than the current
> node. However it doesn't guarantee that dst_nid has the numa capacity
> to move. It also doesn't guarantee that dst_nid has the best_cpu which
> is the cpu/node ideal for node migration.
>
> Lets consider faults on a 4 node system with group weight numbers
> in different nodes being in 0 < 1 < 2 < 3 proportion. Consider the task
> is running on 3 and 0 is its preferred node but its capacity is full.
> Consider nodes 1, 2 and 3 have capacity. Then the task should be
> migrated to node 1. Currently the task gets moved to node 2. env.dst_nid
> points to the last node whose faults were greater than current node.
>
> Modify to set the preferred node based of best_cpu. Earlier setting
> preferred node was skipped if nr_active_nodes is 1. This could result in
> the task being moved out of the preferred node to a random node during
> regular load balancing.
>
> Also while modifying task_numa_migrate(), use sched_setnuma to set
> preferred node. This ensures out numa accounting is correct.
>
> Running SPECjbb2005 on a 4 node machine and comparing bops/JVM
> JVMS LAST_PATCH WITH_PATCH %CHANGE
> 16 25122.9 25549.6 1.698
> 1 73850 73190 -0.89
>
> Running SPECjbb2005 on a 16 node machine and comparing bops/JVM
> JVMS LAST_PATCH WITH_PATCH %CHANGE
> 8 105930 113437 7.08676
> 1 178624 196130 9.80047
>
> (numbers from v1 based on v4.17-rc5)
> Testcase Time: Min Max Avg StdDev
> numa01.sh Real: 435.78 653.81 534.58 83.20
> numa01.sh Sys: 121.93 187.18 145.90 23.47
> numa01.sh User: 37082.81 51402.80 43647.60 5409.75
> numa02.sh Real: 60.64 61.63 61.19 0.40
> numa02.sh Sys: 14.72 25.68 19.06 4.03
> numa02.sh User: 5210.95 5266.69 5233.30 20.82
> numa03.sh Real: 746.51 808.24 780.36 23.88
> numa03.sh Sys: 97.26 108.48 105.07 4.28
> numa03.sh User: 58956.30 61397.05 60162.95 1050.82
> numa04.sh Real: 465.97 519.27 484.81 19.62
> numa04.sh Sys: 304.43 359.08 334.68 20.64
> numa04.sh User: 37544.16 41186.15 39262.44 1314.91
> numa05.sh Real: 411.57 457.20 433.29 16.58
> numa05.sh Sys: 230.05 435.48 339.95 67.58
> numa05.sh User: 33325.54 36896.31 35637.84 1222.64
>
> Testcase Time: Min Max Avg StdDev %Change
> numa01.sh Real: 506.35 794.46 599.06 104.26 -10.76%
> numa01.sh Sys: 150.37 223.56 195.99 24.94 -25.55%
> numa01.sh User: 43450.69 61752.04 49281.50 6635.33 -11.43%
> numa02.sh Real: 60.33 62.40 61.31 0.90 -0.195%
> numa02.sh Sys: 18.12 31.66 24.28 5.89 -21.49%
> numa02.sh User: 5203.91 5325.32 5260.29 49.98 -0.513%
> numa03.sh Real: 696.47 853.62 745.80 57.28 4.6339%
> numa03.sh Sys: 85.68 123.71 97.89 13.48 7.3347%
> numa03.sh User: 55978.45 66418.63 59254.94 3737.97 1.5323%
> numa04.sh Real: 444.05 514.83 497.06 26.85 -2.464%
> numa04.sh Sys: 230.39 375.79 316.23 48.58 5.8343%
> numa04.sh User: 35403.12 41004.10 39720.80 2163.08 -1.153%
> numa05.sh Real: 423.09 460.41 439.57 13.92 -1.428%
> numa05.sh Sys: 287.38 480.15 369.37 68.52 -7.964%
> numa05.sh User: 34732.12 38016.80 36255.85 1070.51 -1.704%
>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

Acked-by: Mel Gorman <mgorman@techsingularity.net>

Also minor comment below;

> ---
> Changelog v1->v2:
> Fix setting sched_setnuma under !sd pointed by Peter Zijlstra.
> Modify commit message to describe the reason for change.
>
> kernel/sched/fair.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 285d7ae..2366fda2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1726,7 +1726,7 @@ static int task_numa_migrate(struct task_struct *p)
> * elsewhere, so there is no point in (re)trying.
> */
> if (unlikely(!sd)) {
> - p->numa_preferred_nid = task_node(p);
> + sched_setnuma(p, task_node(p));
> return -EINVAL;
> }
>

That looks like it had the potential to corrupt the stats managed by
account_numa_enqueue/dequeue :/

--
Mel Gorman
SUSE Labs

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