linux-kernel - [PATCH 2/2] kernel/smp: Use make csd_lock_wait be smp_cond

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Date:	Wed,  9 Mar 2016 17:55:36 -0800
From:	Davidlohr Bueso <dbueso@...e.de>
To:	mingo@...nel.org
Cc:	peterz@...radead.org, dave@...olabs.net,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 2/2] kernel/smp: Use make csd_lock_wait be smp_cond_acquire

From: Davidlohr Bueso <dave@...olabs>

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@...e.de>
---
 kernel/smp.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index c91e00178f8f..74165443c240 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)
-- 
2.1.4