lkml.org 
[lkml]   [2011]   [Jul]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:sched/core] sched: Simplify mutex_spin_on_owner()
Commit-ID:  307bf9803f25a8a3f53c1012110fb74e2f893eb0
Gitweb: http://git.kernel.org/tip/307bf9803f25a8a3f53c1012110fb74e2f893eb0
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Fri, 10 Jun 2011 15:08:55 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 1 Jul 2011 10:39:07 +0200

sched: Simplify mutex_spin_on_owner()

It does not make sense to rcu_read_lock/unlock() in every loop
iteration while spinning on the mutex.

Move the rcu protection outside the loop. Also simplify the
return path to always check for lock->owner == NULL which
meets the requirements of both owner changed and need_resched()
caused loop exits.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1106101458350.11814@ionos
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched.c | 25 +++++++++----------------
1 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 5925275..e355ee7 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4306,11 +4306,8 @@ EXPORT_SYMBOL(schedule);

static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
{
- bool ret = false;
-
- rcu_read_lock();
if (lock->owner != owner)
- goto fail;
+ return false;

/*
* Ensure we emit the owner->on_cpu, dereference _after_ checking
@@ -4320,11 +4317,7 @@ static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
*/
barrier();

- ret = owner->on_cpu;
-fail:
- rcu_read_unlock();
-
- return ret;
+ return owner->on_cpu;
}

/*
@@ -4336,21 +4329,21 @@ int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
if (!sched_feat(OWNER_SPIN))
return 0;

+ rcu_read_lock();
while (owner_running(lock, owner)) {
if (need_resched())
- return 0;
+ break;

arch_mutex_cpu_relax();
}
+ rcu_read_unlock();

/*
- * If the owner changed to another task there is likely
- * heavy contention, stop spinning.
+ * We break out the loop above on need_resched() and when the
+ * owner changed, which is a sign for heavy contention. Return
+ * success only when lock->owner is NULL.
*/
- if (lock->owner)
- return 0;
-
- return 1;
+ return lock->owner == NULL;
}
#endif


\
 
 \ /
  Last update: 2011-07-01 17:19    [W:0.085 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site