On Fri, 2012-08-10 at 16:25 +0900, Namhyung Kim wrote:
> From: Namhyung Kim <namhyung....@lge.com>
>
> When sync wakeup happens and there's the waker task running alone,
> select the target cpu as if it's already idle.
Ouch. That defeats the purpose of select_idle_sibling(). Just because
we're doing a sync wakeup does not mean there's no convertible overlap,
nor that the waker is really really going to take a nap immediately. A
lot of the places that benefit up to and including hugely from looking
for an idle shared cache to wake to do sync wakeups.
> Cc: Mike Galbraith <efa...@gmx.de>
> Cc: Suresh Siddha <suresh.b.sid...@intel.com>
> Signed-off-by: Namhyung Kim <namhy...@kernel.org>
> ---
> kernel/sched/fair.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d0cc03b3e70b..64b68bc82b52 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2632,7 +2632,7 @@ find_idlest_cpu(struct sched_group *group, struct
> task_struct *p, int this_cpu)
> /*
> * Try and locate an idle CPU in the sched_domain.
> */
> -static int select_idle_sibling(struct task_struct *p, int target)
> +static int select_idle_sibling(struct task_struct *p, int target, int sync)
> {
> int cpu = smp_processor_id();
> int prev_cpu = task_cpu(p);
> @@ -2646,6 +2646,13 @@ static int select_idle_sibling(struct task_struct *p,
> int target)
> return cpu;
>
> /*
> + * If the task is going to be woken-up on this cpu and there's only
> + * the sync-waker running, then it is the right target.
> + */
> + if (target == cpu && sync && this_rq()->nr_running == 1)
> + return cpu;
> +
> + /*
> * If the task is going to be woken-up on the cpu where it previously
> * ran and if it is currently idle, then it the right target.
> */
> @@ -2748,7 +2755,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag,
> int wake_flags)
> if (cpu == prev_cpu || wake_affine(affine_sd, p, sync))
> prev_cpu = cpu;
>
> - new_cpu = select_idle_sibling(p, prev_cpu);
> + new_cpu = select_idle_sibling(p, prev_cpu, sync);
> goto unlock;
> }
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
