Merge branch 'core/iter-div' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core/iter-div' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  always_inline timespec_add_ns
  add an inlined version of iter_div_u64_rem
  common implementation of iterative div/mod

4 files changed, 40 insertions, 20 deletions

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index c39e1a5aa241..52b2e3856980 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -12,6 +12,7 @@
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
 #include <linux/kernel_stat.h>
+#include <linux/math64.h>
 
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
@@ -150,11 +151,7 @@ static void do_stolen_accounting(void)
         if (stolen < 0)
                 stolen = 0;
 
-        ticks = 0;
-        while (stolen >= NS_PER_TICK) {
-                ticks++;
-                stolen -= NS_PER_TICK;
-        }
+        ticks = iter_div_u64_rem(stolen, NS_PER_TICK, &stolen);
         __get_cpu_var(residual_stolen) = stolen;
         account_steal_time(NULL, ticks);
 
@@ -166,11 +163,7 @@ static void do_stolen_accounting(void)
         if (blocked < 0)
                 blocked = 0;
 
-        ticks = 0;
-        while (blocked >= NS_PER_TICK) {
-                ticks++;
-                blocked -= NS_PER_TICK;
-        }
+        ticks = iter_div_u64_rem(blocked, NS_PER_TICK, &blocked);
         __get_cpu_var(residual_blocked) = blocked;
         account_steal_time(idle_task(smp_processor_id()), ticks);
 }
diff --git a/include/linux/math64.h b/include/linux/math64.h
index c1a5f81501ff..c87f1528703a 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -81,4 +81,25 @@ static inline s64 div_s64(s64 dividend, s32 divisor)
 }
 #endif
 
+u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder);
+
+static __always_inline u32
+__iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
+{
+        u32 ret = 0;
+
+        while (dividend >= divisor) {
+                /* The following asm() prevents the compiler from
+                   optimising this loop into a modulo operation.  */
+                asm("" : "+rm"(dividend));
+
+                dividend -= divisor;
+                ret++;
+        }
+
+        *remainder = dividend;
+
+        return ret;
+}
+
 #endif /* _LINUX_MATH64_H */
diff --git a/include/linux/time.h b/include/linux/time.h
index d32ef0ad4c0a..e15206a7e82e 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -6,6 +6,7 @@
 #ifdef __KERNEL__
 # include <linux/cache.h>
 # include <linux/seqlock.h>
+# include <linux/math64.h>
 #endif
 
 #ifndef _STRUCT_TIMESPEC
@@ -169,18 +170,13 @@ extern struct timeval ns_to_timeval(const s64 nsec);
  * timespec_add_ns - Adds nanoseconds to a timespec
  * @a:          pointer to timespec to be incremented
  * @ns:         unsigned nanoseconds value to be added
+ *
+ * This must always be inlined because its used from the x86-64 vdso,
+ * which cannot call other kernel functions.
  */
-static inline void timespec_add_ns(struct timespec *a, u64 ns)
+static __always_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++;
-        }
+        a->tv_sec += __iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
         a->tv_nsec = ns;
 }
 #endif /* __KERNEL__ */
diff --git a/lib/div64.c b/lib/div64.c
index bb5bd0c0f030..a111eb8de9cf 100644
--- a/lib/div64.c
+++ b/lib/div64.c
@@ -98,3 +98,13 @@ EXPORT_SYMBOL(div64_u64);
 #endif
 
 #endif /* BITS_PER_LONG == 32 */
+
+/*
+ * Iterative div/mod for use when dividend is not expected to be much
+ * bigger than divisor.
+ */
+u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
+{
+        return __iter_div_u64_rem(dividend, divisor, remainder);
+}
+EXPORT_SYMBOL(iter_div_u64_rem);