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Subject[PATCH] sched/core: Minor optimize ttwu_runnable()
Date
ttwu_runnable() is used as a fast wakeup path when the wakee task
is between set_current_state() and schedule(), in which case all
we need to do is change p->state back to TASK_RUNNING. So we don't
need to update_rq_clock() and check_preempt_curr() in this case.

Some performance numbers using mmtests/perfpipe on Intel Xeon server:

linux-next patched
Min Time 8.67 ( 0.00%) 8.66 ( 0.13%)
1st-qrtle Time 8.83 ( 0.00%) 8.72 ( 1.19%)
2nd-qrtle Time 8.90 ( 0.00%) 8.76 ( 1.57%)
3rd-qrtle Time 8.98 ( 0.00%) 8.82 ( 1.82%)
Max-1 Time 8.67 ( 0.00%) 8.66 ( 0.13%)
Max-5 Time 8.67 ( 0.00%) 8.66 ( 0.13%)
Max-10 Time 8.79 ( 0.00%) 8.69 ( 1.09%)
Max-90 Time 9.01 ( 0.00%) 8.84 ( 1.94%)
Max-95 Time 9.02 ( 0.00%) 8.85 ( 1.86%)
Max-99 Time 9.02 ( 0.00%) 8.88 ( 1.56%)
Max Time 9.59 ( 0.00%) 8.89 ( 7.29%)
Amean Time 8.92 ( 0.00%) 8.77 * 1.65%*

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
kernel/sched/core.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 87c9cdf37a26..3785418de127 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3718,9 +3718,8 @@ static int ttwu_runnable(struct task_struct *p, int wake_flags)

rq = __task_rq_lock(p, &rf);
if (task_on_rq_queued(p)) {
- /* check_preempt_curr() may use rq clock */
- update_rq_clock(rq);
- ttwu_do_wakeup(rq, p, wake_flags, &rf);
+ WRITE_ONCE(p->__state, TASK_RUNNING);
+ trace_sched_wakeup(p);
ret = 1;
}
__task_rq_unlock(rq, &rf);
--
2.37.2
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