lkml.org 
[lkml]   [2012]   [Jan]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH v2] sched: Accelerate "pick_next_entity" under special condition
From: wangyun <wangyun@linux.vnet.ibm.com>

In original code, we get the next entity in this way:

if(condition1)
result=value1;
if(condition2)
result=value2;
if(condition3)
result=value3;
return result;
So if condition3 is true, we will get value3, but still
need to check condition1 and condition2, this will waste
our time.

This patch will change the way like:

if(condition3) {
result=value3;
goto out;
}
if(condition2) {
result=value2;
goto out;
}
if(condition1) {
result=value1;
goto out;
}
out:
return result;

So we can avoid check condition2 and condition1 when
condition3 is true now.

v2:
1. do not use ugly macro any more.
2. add more description.

Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
---
kernel/sched/fair.c | 26 +++++++++++++++-----------
1 files changed, 15 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 84adb2d..e8a72b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1308,29 +1308,33 @@ static struct sched_entity
*pick_next_entity(struct cfs_rq *cfs_rq)
struct sched_entity *left = se;

/*
- * Avoid running the skip buddy, if running something else can
- * be done without getting too unfair.
+ * Someone really wants this to run. If it's not unfair, run it.
*/
- if (cfs_rq->skip == se) {
- struct sched_entity *second = __pick_next_entity(se);
- if (second && wakeup_preempt_entity(second, left) < 1)
- se = second;
+ if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) {
+ se = cfs_rq->next;
+ goto out;
}

/*
* Prefer last buddy, try to return the CPU to a preempted task.
*/
- if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
+ if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) {
se = cfs_rq->last;
+ goto out;
+ }

/*
- * Someone really wants this to run. If it's not unfair, run it.
+ * Avoid running the skip buddy, if running something else can
+ * be done without getting too unfair.
*/
- if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
- se = cfs_rq->next;
+ if (cfs_rq->skip == se) {
+ struct sched_entity *second = __pick_next_entity(se);
+ if (second && wakeup_preempt_entity(second, left) < 1)
+ se = second;
+ }

+out:
clear_buddies(cfs_rq, se);
-
return se;
}

--
1.7.4.1


\
 
 \ /
  Last update: 2012-01-17 03:39    [from the cache]
©2003-2011 Jasper Spaans