linux-kernel - [PATCH] Prevent the loop in timespec_add

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Date:	Fri, 22 Feb 2008 22:40:45 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	linux-kernel@...r.kernel.org
Cc:	Segher Boessenkool <segher@...nel.crashing.org>
Subject: [PATCH] Prevent the loop in timespec_add_ns() to be optimised away

...since some architectures don't support __udivdi3() (and
we don't want to use that, anyway).

Signed-off-by: Segher Boessenkool <segher@...nel.crashing.org>
---
 include/linux/time.h |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/include/linux/time.h b/include/linux/time.h
index 2091a19..d32ef0a 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -174,6 +174,10 @@ static inline void timespec_add_ns(struct timespec *a, u64 ns)
 {
 	ns += a->tv_nsec;
 	while(unlikely(ns >= NSEC_PER_SEC)) {
+		/* The following asm() prevents the compiler from
+		 * optimising this loop into a modulo operation.  */
+		asm("" : "+r"(ns));
+
 		ns -= NSEC_PER_SEC;
 		a->tv_sec++;
 	}
-- 
1.5.4.2.184.gb23b

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