From 8bd0fe749c98e67ee4150b6eaf3b66f361413ec0 Mon Sep 17 00:00:00 2001
From: Salman Qazi <sqazi@google.com>
Date: Fri, 9 Mar 2012 16:41:01 -0800
Subject: [PATCH] --- yaml --- r: 288767 b: refs/heads/master c:
 9993bc635d01a6ee7f6b833b4ee65ce7c06350b1 h: refs/heads/master i:   288765:
 cb5407fede03c372b07ae080c44ec94423e412c8   288763:
 569c3f9d1b0dbb7216ee596f733a26d6b80ab40e   288759:
 96e02350090689e2bf60e56ffbc6394aa092c4c9   288751:
 b9a20c8b0c30002a5855d120b6029d1c043c1df2   288735:
 373226b5c95a72c5aeeb8f901199b9d6e7c11791   288703:
 783d1710c2438bf7a2316af5b8ccbaabc56f2187   288639:
 04077cd75932a81bcf262cfe98fa59d57042d2d3   288511:
 c86ec1a70f3d84b21dda5fcd5600fc576d6aeaeb   288255:
 5852ec89ed1ae6f0d75518d954fe38328e63f157   287743:
 4f58ce1bbf10f99c33a162bc9a5cbb662052a2a7   286719:
 66d4c0fd3b051803633a7e1f7e2fb3b66e0c2fe6 v: v3

---
 [refs]                             |  2 +-
 trunk/arch/x86/include/asm/timer.h |  8 ++------
 trunk/arch/x86/kernel/tsc.c        |  3 ++-
 trunk/include/linux/kernel.h       | 13 +++++++++++++
 4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/[refs] b/[refs]
index 82eb0ef52b1a..d13ebf2f9e89 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 47258cf3c4aa5d56e678bafe0dd0d03ddd980b88
+refs/heads/master: 9993bc635d01a6ee7f6b833b4ee65ce7c06350b1
diff --git a/trunk/arch/x86/include/asm/timer.h b/trunk/arch/x86/include/asm/timer.h
index 431793e5d484..34baa0eb5d0c 100644
--- a/trunk/arch/x86/include/asm/timer.h
+++ b/trunk/arch/x86/include/asm/timer.h
@@ -57,14 +57,10 @@ DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
 
 static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
 {
-	unsigned long long quot;
-	unsigned long long rem;
 	int cpu = smp_processor_id();
 	unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
-	quot = (cyc >> CYC2NS_SCALE_FACTOR);
-	rem = cyc & ((1ULL << CYC2NS_SCALE_FACTOR) - 1);
-	ns += quot * per_cpu(cyc2ns, cpu) +
-		((rem * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR);
+	ns += mult_frac(cyc, per_cpu(cyc2ns, cpu),
+			(1UL << CYC2NS_SCALE_FACTOR));
 	return ns;
 }
 
diff --git a/trunk/arch/x86/kernel/tsc.c b/trunk/arch/x86/kernel/tsc.c
index a62c201c97ec..183c5925a9fe 100644
--- a/trunk/arch/x86/kernel/tsc.c
+++ b/trunk/arch/x86/kernel/tsc.c
@@ -620,7 +620,8 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
 
 	if (cpu_khz) {
 		*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
-		*offset = ns_now - (tsc_now * *scale >> CYC2NS_SCALE_FACTOR);
+		*offset = ns_now - mult_frac(tsc_now, *scale,
+					     (1UL << CYC2NS_SCALE_FACTOR));
 	}
 
 	sched_clock_idle_wakeup_event(0);
diff --git a/trunk/include/linux/kernel.h b/trunk/include/linux/kernel.h
index e8343422240a..d801acb5e680 100644
--- a/trunk/include/linux/kernel.h
+++ b/trunk/include/linux/kernel.h
@@ -85,6 +85,19 @@
 }							\
 )
 
+/*
+ * Multiplies an integer by a fraction, while avoiding unnecessary
+ * overflow or loss of precision.
+ */
+#define mult_frac(x, numer, denom)(			\
+{							\
+	typeof(x) quot = (x) / (denom);			\
+	typeof(x) rem  = (x) % (denom);			\
+	(quot * (numer)) + ((rem * (numer)) / (denom));	\
+}							\
+)
+
+
 #define _RET_IP_		(unsigned long)__builtin_return_address(0)
 #define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })