Subject: sched: Avoid select_idle_sibling() for wake_affine(.sync=true) From: Peter Zijlstra <[email protected]> Date: Wed Sep 25 08:28:39 CEST 2013
When a task is the only running task and does a sync wakeup; avoid going through select_idle_sibling() as it doesn't know the current CPU is going to be idle shortly. Without this two sync wakers will ping-pong between CPUs for no reason. Suggested-by: Rik van Riel <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> --- kernel/sched/fair.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3461,6 +3461,16 @@ select_task_rq_fair(struct task_struct * if (cpu != prev_cpu && wake_affine(affine_sd, p, sync)) prev_cpu = cpu; + /* + * Don't bother with select_idle_sibling() in the case of a sync wakeup + * where we know the only running task will soon go away. Going + * through select_idle_sibling will only lead to pointless ping-pong. + */ + if (sync && prev_cpu == cpu && cpu_rq(cpu)->nr_running == 1) { + new_cpu = cpu; + goto unlock; + } + new_cpu = select_idle_sibling(p, prev_cpu); goto unlock; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
