---

yaml --- r: 288767 b: refs/heads/master c: 9993bc6 h: refs/heads/master i: 288765: cb5407f 288763: 569c3f9 288759: 96e0235 288751: b9a20c8 288735: 373226b 288703: 783d171 288639: 04077cd 288511: c86ec1a 288255: 5852ec8 287743: 4f58ce1 286719: 66d4c0f v: v3
git-mirror · Mar 13, 2012 · 8bd0fe7 · 8bd0fe7
1 parent e21f3bc
commit 8bd0fe7
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Showing 4 changed files with 18 additions and 8 deletions.
diff --git 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
@@ -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
@@ -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
@@ -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; })