[tip:sched/core] sched: Add new wakeup preemption mode: WAKEUP_RUNNING

tip-bot for Peter Zijlstra
2009-09-17T08:19:16Z

Commit-ID: ad4b78bbcbab66998b05d422ac6106b645796e54
Gitweb: http://git.kernel.org/tip/ad4b78bbcbab66998b05d422ac6106b645796e54
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 16 Sep 2009 12:31:31 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 17 Sep 2009 10:17:25 +0200

sched: Add new wakeup preemption mode: WAKEUP_RUNNING

Create a new wakeup preemption mode, preempt towards tasks that run
shorter on avg. It sets next buddy to be sure we actually run the task
we preempted for.

Test results:

root@twins:~# while :; do :; done &
[1] 6537
root@twins:~# while :; do :; done &
[2] 6538
root@twins:~# while :; do :; done &
[3] 6539
root@twins:~# while :; do :; done &
[4] 6540

root@twins:/home/peter# ./latt -c4 sleep 4
Entries: 48 (clients=4)

Averages:
------------------------------
Max 4750 usec
Avg 497 usec
Stdev 737 usec

root@twins:/home/peter# echo WAKEUP_RUNNING > /debug/sched_features

root@twins:/home/peter# ./latt -c4 sleep 4
Entries: 48 (clients=4)

Averages:
------------------------------
Max 14 usec
Avg 5 usec
Stdev 3 usec

Disabled by default - needs more testing.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <new-submission>

---
include/linux/sched.h | 2 ++
kernel/sched.c | 17 ++++++++++-------
kernel/sched_debug.c | 1 +
kernel/sched_fair.c | 14 +++++++++++---
kernel/sched_features.h | 5 +++++
5 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b4a39bb..8af3d24 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1113,6 +1113,8 @@ struct sched_entity {
u64 start_runtime;
u64 avg_wakeup;

+ u64 avg_running;
+
#ifdef CONFIG_SCHEDSTATS
u64 wait_start;
u64 wait_max;
diff --git a/kernel/sched.c b/kernel/sched.c
index 969dfae..3bb4ea2 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2458,6 +2458,7 @@ static void __sched_fork(struct task_struct *p)
p->se.avg_overlap = 0;
p->se.start_runtime = 0;
p->se.avg_wakeup = sysctl_sched_wakeup_granularity;
+ p->se.avg_running = 0;

#ifdef CONFIG_SCHEDSTATS
p->se.wait_start = 0;
@@ -5310,14 +5311,13 @@ static inline void schedule_debug(struct task_struct *prev)
#endif
}

-static void put_prev_task(struct rq *rq, struct task_struct *prev)
+static void put_prev_task(struct rq *rq, struct task_struct *p)
{
- if (prev->state == TASK_RUNNING) {
- u64 runtime = prev->se.sum_exec_runtime;
+ u64 runtime = p->se.sum_exec_runtime - p->se.prev_sum_exec_runtime;

- runtime -= prev->se.prev_sum_exec_runtime;
- runtime = min_t(u64, runtime, 2*sysctl_sched_migration_cost);
+ update_avg(&p->se.avg_running, runtime);

+ if (p->state == TASK_RUNNING) {
/*
* In order to avoid avg_overlap growing stale when we are
* indeed overlapping and hence not getting put to sleep, grow
@@ -5327,9 +5327,12 @@ static void put_prev_task(struct rq *rq, struct task_struct *prev)
* correlates to the amount of cache footprint a task can
* build up.
*/
- update_avg(&prev->se.avg_overlap, runtime);
+ runtime = min_t(u64, runtime, 2*sysctl_sched_migration_cost);
+ update_avg(&p->se.avg_overlap, runtime);
+ } else {
+ update_avg(&p->se.avg_running, 0);
}
- prev->sched_class->put_prev_task(rq, prev);
+ p->sched_class->put_prev_task(rq, p);
}

/*
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 5ddbd08..efb8440 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -395,6 +395,7 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
PN(se.sum_exec_runtime);
PN(se.avg_overlap);
PN(se.avg_wakeup);
+ PN(se.avg_running);

nr_switches = p->nvcsw + p->nivcsw;

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index c741cd9..3e6f78c 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1605,9 +1605,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
return;
}

- if (!sched_feat(WAKEUP_PREEMPT))
- return;
-
if ((sched_feat(WAKEUP_SYNC) && sync) ||
(sched_feat(WAKEUP_OVERLAP) &&
(se->avg_overlap < sysctl_sched_migration_cost &&
@@ -1616,6 +1613,17 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
return;
}

+ if (sched_feat(WAKEUP_RUNNING)) {
+ if (pse->avg_running < se->avg_running) {
+ set_next_buddy(pse);
+ resched_task(curr);
+ return;
+ }
+ }
+
+ if (!sched_feat(WAKEUP_PREEMPT))
+ return;
+
find_matching_se(&se, &pse);

BUG_ON(!pse);
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index d5059fd..0d94083 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -54,6 +54,11 @@ SCHED_FEAT(WAKEUP_SYNC, 0)
SCHED_FEAT(WAKEUP_OVERLAP, 0)

/*
+ * Wakeup preemption towards tasks that run short
+ */
+SCHED_FEAT(WAKEUP_RUNNING, 0)
+
+/*
* Use the SYNC wakeup hint, pipes and the likes use this to indicate
* the remote end is likely to consume the data we just wrote, and
* therefore has cache benefit from being placed on the same cpu, see