linux-kernel - [PATCH] lockref: Relax in cmpxchg loop

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Message-Id: <0129530@agluck-desk.sc.intel.com>
Date:	Tue, 3 Sep 2013 14:49:49 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] lockref: Relax in cmpxchg loop

While we are likley to succeed and break out of this loop, it isn't
guaranteed.  We should be power and thread friendly if we do have to
go around for a second (or third, or more) attempt.

Signed-off-by: Tony Luck <tony.luck@...el.com>

---

diff --git a/lib/lockref.c b/lib/lockref.c
index 7819c2d..9d76f40 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -19,6 +19,7 @@
 		if (likely(old.lock_count == prev.lock_count)) {		\
 			SUCCESS;						\
 		}								\
+		cpu_relax();							\
 	}									\
 } while (0)
 
-- 
1.8.1.4

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