From 491f6f8e5fd9a57aaf03b6d6e3e153f1c27d8a46 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Mon, 23 Sep 2013 12:59:56 +0200
Subject: [PATCH] lockref: use arch_mutex_cpu_relax() in CMPXCHG_LOOP()
Make use of arch_mutex_cpu_relax() so architectures can override the
default cpu_relax() semantics.
This is especially useful for s390, where cpu_relax() means that we
yield() the current (virtual) cpu and therefore is very expensive,
and would contradict the whole purpose of the lockless cmpxchg loop.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
lib/lockref.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/lib/lockref.c b/lib/lockref.c
index e294ae445c9ab..6f9d434c1521e 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -11,6 +11,14 @@
# define cmpxchg64_relaxed cmpxchg64
#endif
+/*
+ * Allow architectures to override the default cpu_relax() within CMPXCHG_LOOP.
+ * This is useful for architectures with an expensive cpu_relax().
+ */
+#ifndef arch_mutex_cpu_relax
+# define arch_mutex_cpu_relax() cpu_relax()
+#endif
+
/*
* Note that the "cmpxchg()" reloads the "old" value for the
* failure case.
@@ -28,7 +36,7 @@
if (likely(old.lock_count == prev.lock_count)) { \
SUCCESS; \
} \
- cpu_relax(); \
+ arch_mutex_cpu_relax(); \
} \
} while (0)
--
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