time: Allow gcc to fold constants when possible

[cascardo/linux.git] / include / linux / jiffies.h

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 9527ddb..5e75af6 100644 (file)
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -343,12 +343,24 @@ static inline unsigned long _msecs_to_jiffies(const unsigned int m)
  *   handling any 32-bit overflows.
  *   for the details see __msecs_to_jiffies()
  *
- * the HZ range specific helpers _msecs_to_jiffies() are called from
- * __msecs_to_jiffies().
+ * msecs_to_jiffies() checks for the passed in value being a constant
+ * via __builtin_constant_p() allowing gcc to eliminate most of the
+ * code, __msecs_to_jiffies() is called if the value passed does not
+ * allow constant folding and the actual conversion must be done at
+ * runtime.
+ * the HZ range specific helpers _msecs_to_jiffies() are called both
+ * directly here and from __msecs_to_jiffies() in the case where
+ * constant folding is not possible.
  */
 static inline unsigned long msecs_to_jiffies(const unsigned int m)
 {
-       return __msecs_to_jiffies(m);
+       if (__builtin_constant_p(m)) {
+               if ((int)m < 0)
+                       return MAX_JIFFY_OFFSET;
+               return _msecs_to_jiffies(m);
+       } else {
+               return __msecs_to_jiffies(m);
+       }
 }
 
 extern unsigned long usecs_to_jiffies(const unsigned int u);