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SubjectRe: [PATCH] schedule: use unlikely()

* Mikulas Patocka <mpatocka@redhat.com> wrote:

> A small patch for schedule(), so that the code goes straght in the common
> case.
>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
>
> ---
> include/linux/blkdev.h | 2 +-
> kernel/sched/core.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/include/linux/blkdev.h
> ===================================================================
> --- linux-2.6.orig/include/linux/blkdev.h
> +++ linux-2.6/include/linux/blkdev.h
> @@ -1308,7 +1308,7 @@ static inline bool blk_needs_flush_plug(
> {
> struct blk_plug *plug = tsk->plug;
>
> - return plug &&
> + return unlikely(plug != NULL) &&
> (!list_empty(&plug->list) ||
> !list_empty(&plug->mq_list) ||
> !list_empty(&plug->cb_list));

That's an unrelated change.

> Index: linux-2.6/kernel/sched/core.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched/core.c
> +++ linux-2.6/kernel/sched/core.c
> @@ -3405,7 +3405,7 @@ void __noreturn do_task_dead(void)
>
> static inline void sched_submit_work(struct task_struct *tsk)
> {
> - if (!tsk->state || tsk_is_pi_blocked(tsk))
> + if (!tsk->state || unlikely(tsk_is_pi_blocked(tsk)))
> return;
> /*
> * If we are going to sleep and we have plugged IO queued,

Do these changes actually change the generated assembly code?

Thanks,

Ingo

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