2013-07-10 10:30:29

by Kirill Tkhai

Subject: [PATCH] sched: Skip update_rq_clock() in enqueue_task() following right after dequeue_task()

Add new flag ENQUEUE_NO_CLK to skip microscopic rq->clock update.

This update is less even than in places where skip_clock_update is used.

Signed-off-by: Kirill Tkhai <[email protected]>
CC: Ingo Molnar <[email protected]>
CC: Peter Zijlstra <[email protected]>
CC: Steven Rostedt <[email protected]>
---
kernel/sched/core.c | 12 +++++++-----
kernel/sched/sched.h | 1 +
2 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9d06ad6..0b99057 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -764,7 +764,9 @@ static void set_load_weight(struct task_struct *p)

static void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
- update_rq_clock(rq);
+ if (!(flags & ENQUEUE_NO_CLK))
+ update_rq_clock(rq);
+
sched_info_queued(p);
p->sched_class->enqueue_task(rq, p, flags);
}
@@ -3107,7 +3109,7 @@ void set_user_nice(struct task_struct *p, long nice)
delta = p->prio - old_prio;

if (on_rq) {
- enqueue_task(rq, p, 0);
+ enqueue_task(rq, p, ENQUEUE_NO_CLK);
/*
* If the task increased its priority or is running and
* lowered its priority, then reschedule its CPU:
@@ -3414,7 +3416,7 @@ recheck:
if (running)
p->sched_class->set_curr_task(rq);
if (on_rq)
- enqueue_task(rq, p, 0);
+ enqueue_task(rq, p, ENQUEUE_NO_CLK);

check_class_changed(rq, p, prev_class, oldprio);
task_rq_unlock(rq, p, &flags);
@@ -6562,7 +6564,7 @@ static void normalize_task(struct rq *rq, struct task_struct *p)
dequeue_task(rq, p, 0);
__setscheduler(rq, p, SCHED_NORMAL, 0);
if (on_rq) {
- enqueue_task(rq, p, 0);
+ enqueue_task(rq, p, ENQUEUE_NO_CLK);
resched_task(rq->curr);
}

@@ -6777,7 +6779,7 @@ void sched_move_task(struct task_struct *tsk)
if (unlikely(running))
tsk->sched_class->set_curr_task(rq);
if (on_rq)
- enqueue_task(rq, tsk, 0);
+ enqueue_task(rq, tsk, ENQUEUE_NO_CLK);

task_rq_unlock(rq, tsk, &flags);
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ef0a7b2..4b8dfd7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -957,6 +957,7 @@ static const u32 prio_to_wmult[40] = {
#else
#define ENQUEUE_WAKING 0
#endif
+#define ENQUEUE_NO_CLK 8 /* skip update_rq_clock() */

#define DEQUEUE_SLEEP 1