Messages in this thread Patch in this message | | | From | Srikar Dronamraju <> | Subject | [PATCH v2 10/19] sched/numa: Stop multiple tasks from moving to the cpu at the same time | Date | Wed, 20 Jun 2018 22:32:51 +0530 |
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Task migration under numa balancing can happen in parallel. More than one task might choose to migrate to the same cpu at the same time. This can result in - During task swap, choosing a task that was not part of the evaluation. - During task swap, task which just got moved into its preferred node, moving to a completely different node. - During task swap, task failing to move to the preferred node, will have to wait an extra interval for the next migrate opportunity. - During task movement, multiple task movements can cause load imbalance.
This problem is more likely if there are more cores per node or more nodes in the system.
Use a per run-queue variable to check if numa-balance is active on the run-queue.
Running SPECjbb2005 on a 4 node machine and comparing bops/JVM JVMS LAST_PATCH WITH_PATCH %CHANGE 16 25226.6 25436.1 0.83 1 73326 74031 0.96
Running SPECjbb2005 on a 16 node machine and comparing bops/JVM JVMS LAST_PATCH WITH_PATCH %CHANGE 8 108750 110355 1.475 1 183115 178401 -2.57
(numbers from v1 based on v4.17-rc5) Testcase Time: Min Max Avg StdDev numa01.sh Real: 414.64 819.20 556.08 147.70 numa01.sh Sys: 77.52 205.04 139.40 52.05 numa01.sh User: 37043.24 61757.88 45517.48 9290.38 numa02.sh Real: 60.80 63.32 61.63 0.88 numa02.sh Sys: 17.35 39.37 25.71 7.33 numa02.sh User: 5213.79 5374.73 5268.90 55.09 numa03.sh Real: 780.09 948.64 831.43 63.02 numa03.sh Sys: 104.96 136.92 116.31 11.34 numa03.sh User: 60465.42 73339.78 64368.03 4700.14 numa04.sh Real: 412.60 681.92 521.29 96.64 numa04.sh Sys: 210.32 314.10 251.77 37.71 numa04.sh User: 34026.38 45581.20 38534.49 4198.53 numa05.sh Real: 394.79 439.63 411.35 16.87 numa05.sh Sys: 238.32 330.09 292.31 38.32 numa05.sh User: 33456.45 34876.07 34138.62 609.45
Testcase Time: Min Max Avg StdDev %Change numa01.sh Real: 434.84 676.90 550.53 106.24 1.008% numa01.sh Sys: 125.98 217.34 179.41 30.35 -22.3% numa01.sh User: 38318.48 53789.56 45864.17 6620.80 -0.75% numa02.sh Real: 60.06 61.27 60.59 0.45 1.716% numa02.sh Sys: 14.25 17.86 16.09 1.28 59.78% numa02.sh User: 5190.13 5225.67 5209.24 13.19 1.145% numa03.sh Real: 748.21 960.25 823.15 73.51 1.005% numa03.sh Sys: 96.68 122.10 110.42 11.29 5.334% numa03.sh User: 58222.16 72595.27 63552.22 5048.87 1.283% numa04.sh Real: 433.08 630.55 499.30 68.15 4.404% numa04.sh Sys: 245.22 386.75 306.09 63.32 -17.7% numa04.sh User: 35014.68 46151.72 38530.26 3924.65 0.010% numa05.sh Real: 394.77 410.07 401.41 5.99 2.476% numa05.sh Sys: 212.40 301.82 256.23 35.41 14.08% numa05.sh User: 33224.86 34201.40 33665.61 313.40 1.405%
Acked-by: Mel Gorman <mgorman@techsingularity.net> Reviewed-by: Rik van Riel <riel@surriel.com> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> --- kernel/sched/fair.c | 17 +++++++++++++++++ kernel/sched/sched.h | 1 + 2 files changed, 18 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0d0248b..50c7727 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1478,6 +1478,16 @@ struct task_numa_env { static void task_numa_assign(struct task_numa_env *env, struct task_struct *p, long imp) { + struct rq *rq = cpu_rq(env->dst_cpu); + + if (xchg(&rq->numa_migrate_on, 1)) + return; + + if (env->best_cpu != -1) { + rq = cpu_rq(env->best_cpu); + WRITE_ONCE(rq->numa_migrate_on, 0); + } + if (env->best_task) put_task_struct(env->best_task); if (p) @@ -1533,6 +1543,9 @@ static void task_numa_compare(struct task_numa_env *env, long moveimp = imp; int dist = env->dist; + if (READ_ONCE(dst_rq->numa_migrate_on)) + return; + rcu_read_lock(); cur = task_rcu_dereference(&dst_rq->curr); if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur))) @@ -1699,6 +1712,7 @@ static int task_numa_migrate(struct task_struct *p) .best_cpu = -1, }; struct sched_domain *sd; + struct rq *best_rq; unsigned long taskweight, groupweight; int nid, ret, dist; long taskimp, groupimp; @@ -1802,14 +1816,17 @@ static int task_numa_migrate(struct task_struct *p) */ p->numa_scan_period = task_scan_start(p); + best_rq = cpu_rq(env.best_cpu); if (env.best_task == NULL) { ret = migrate_task_to(p, env.best_cpu); + WRITE_ONCE(best_rq->numa_migrate_on, 0); if (ret != 0) trace_sched_stick_numa(p, env.src_cpu, env.best_cpu); return ret; } ret = migrate_swap(p, env.best_task, env.best_cpu, env.src_cpu); + WRITE_ONCE(best_rq->numa_migrate_on, 0); if (ret != 0) trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task)); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 52ba2d6..5b15c52 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -756,6 +756,7 @@ struct rq { #ifdef CONFIG_NUMA_BALANCING unsigned int nr_numa_running; unsigned int nr_preferred_running; + unsigned int numa_migrate_on; #endif #define CPU_LOAD_IDX_MAX 5 unsigned long cpu_load[CPU_LOAD_IDX_MAX]; -- 1.8.3.1
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