On Tue, 10 Dec 2013 15:51:35 +0000 Mel Gorman <mgorman@xxxxxxx> wrote:
> This patch adds three tracepoints
> o trace_sched_move_numa when a task is moved to a node
> o trace_sched_swap_numa when a task is swapped with another task
> o trace_sched_stick_numa when a numa-related migration fails
>
> The tracepoints allow the NUMA scheduler activity to be monitored and the
> following high-level metrics can be calculated
>
> o NUMA migrated stuck nr trace_sched_stick_numa
> o NUMA migrated idle nr trace_sched_move_numa
> o NUMA migrated swapped nr trace_sched_swap_numa
> o NUMA local swapped trace_sched_swap_numa src_nid == dst_nid (should never happen)
> o NUMA remote swapped trace_sched_swap_numa src_nid != dst_nid (should == NUMA migrated swapped)
> o NUMA group swapped trace_sched_swap_numa src_ngid == dst_ngid
> Maybe a small number of these are acceptable
> but a high number would be a major surprise.
> It would be even worse if bounces are frequent.
> o NUMA avg task migs. Average number of migrations for tasks
> o NUMA stddev task mig Self-explanatory
> o NUMA max task migs. Maximum number of migrations for a single task
>
> In general the intent of the tracepoints is to help diagnose problems
> where automatic NUMA balancing appears to be doing an excessive amount of
> useless work.
>
> ...
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1272,11 +1272,13 @@ static int task_numa_migrate(struct task_struct *p)
> p->numa_scan_period = task_scan_min(p);
>
> if (env.best_task == NULL) {
> - int ret = migrate_task_to(p, env.best_cpu);
> + if ((ret = migrate_task_to(p, env.best_cpu)) != 0)
> + trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
> return ret;
> }
>
> - ret = migrate_swap(p, env.best_task);
> + if ((ret = migrate_swap(p, env.best_task)) != 0);
I'll zap that semicolon...
> + trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
> put_task_struct(env.best_task);
> return ret;
> }
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