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SubjectRe: [PATCH 4/4] sched/fair: Do not migrate due to a sync wakeup on exit
On Mon, Feb 12, 2018 at 02:58:57PM +0000, Mel Gorman wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 28c8d9c91955..50442697b455 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5710,8 +5710,14 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
> if (idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
> return idle_cpu(prev_cpu) ? prev_cpu : this_cpu;
>
> - if (sync && cpu_rq(this_cpu)->nr_running == 1)
> + if (sync && cpu_rq(this_cpu)->nr_running == 1) {
> + /* Avoid tasks exiting pulling parents to new nodes */
> + if ((current->flags & PF_EXITING) &&
> + !cpus_share_cache(this_cpu, prev_cpu))
> + return prev_cpu;
> +

Cute, but should we not kill @sync right at the source in this case?

Something a little like this?

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5eb3ffc9be84..568ea4ce5b36 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6342,7 +6342,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
int cpu = smp_processor_id();
int new_cpu = prev_cpu;
int want_affine = 0;
- int sync = wake_flags & WF_SYNC;
+ int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING);

if (sd_flag & SD_BALANCE_WAKE) {
record_wakee(p);
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