seqlock: enhance power efficiency

Trying to improve the power efficiency in linux/seqlock.h,
using macros cpu_relaxed_read and cpu_read_relax.

Bug 1440421

Change-Id: I8dcc9dc9c72e5a6848c7823768c76f5d38e9f0d1
Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-on: http://git-master/r/398943
(cherry picked from commit ed77ee4d50641b1a5668545c946cda681c06fcd2)
Reviewed-on: http://git-master/r/422258
GVS: Gerrit_Virtual_Submit
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>
Reviewed-by: Alexander Van Brunt <avanbrunt@nvidia.com>

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 18299057402f1bf9015cff936f9f2a37c01a5896..d4cf5229cc187ce0832152862a7dc6f4d14949e8 100644 (file)
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -29,6 +29,7 @@
 #include <linux/spinlock.h>
 #include <linux/preempt.h>
 #include <asm/processor.h>
+#include <asm/relaxed.h>
 
 /*
  * Version using sequence counter only.
@@ -61,9 +62,9 @@ static inline unsigned __read_seqcount_begin(const seqcount_t *s)
        unsigned ret;
 
 repeat:
-       ret = ACCESS_ONCE(s->sequence);
+       ret = cpu_relaxed_read((volatile u32 *)&s->sequence);
        if (unlikely(ret & 1)) {
-               cpu_relax();
+               cpu_read_relax();
                goto repeat;
        }
        return ret;