[tip:locking/core] locking/csd_lock: Use smp_cond_acquire() in csd_lock_wait()

tip-bot for Davidlohr Bueso
2016-03-10T11:07:00Z

Commit-ID: 38460a2178d225b39ade5ac66586c3733391cf86
Gitweb: http://git.kernel.org/tip/38460a2178d225b39ade5ac66586c3733391cf86
Author: Davidlohr Bueso <dave@stgolabs>
AuthorDate: Wed, 9 Mar 2016 17:55:36 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 10 Mar 2016 10:28:35 +0100

locking/csd_lock: Use smp_cond_acquire() in csd_lock_wait()

We can micro-optimize this call and mildly relax the
barrier requirements by relying on ctrl + rmb, keeping
the acquire semantics. In addition, this is pretty much
the now standard for busy-waiting under such restraints.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1457574936-19065-3-git-send-email-dbueso@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/smp.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index 5099db1..300d293 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -107,8 +107,7 @@ void __init call_function_init(void)
*/
static __always_inline void csd_lock_wait(struct call_single_data *csd)
{
- while (smp_load_acquire(&csd->flags) & CSD_FLAG_LOCK)
- cpu_relax();
+ smp_cond_acquire(!(csd->flags & CSD_FLAG_LOCK));
}

static __always_inline void csd_lock(struct call_single_data *csd)