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authorNicholas Mc Guire <hofrat@osadl.org>2015-05-18 15:19:14 +0300
committerThomas Gleixner <tglx@linutronix.de>2015-05-19 16:14:16 +0300
commitdaa67b4b70568a07fef3cffacb2055891bf42ddb (patch)
tree7ee263ce2b8a48c1f7641e1e6f751b1d9f8e430c /include/linux/jiffies.h
parentca42aaf0c8616cde6161ea4391dff364efeee46a (diff)
downloadlinux-daa67b4b70568a07fef3cffacb2055891bf42ddb.tar.xz
time: Allow gcc to fold constants when possible
To allow constant folding in msecs_to_jiffies() conditionally calls the HZ dependent _msecs_to_jiffies() helpers or, when gcc can not figure out constant folding, __msecs_to_jiffies which is the renamed original msecs_to_jiffies() function. Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org> Cc: Masahiro Yamada <yamada.m@jp.panasonic.com> Cc: Sam Ravnborg <sam@ravnborg.org> Cc: Joe Perches <joe@perches.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Andrew Hunter <ahh@google.com> Cc: Paul Turner <pjt@google.com> Cc: Michal Marek <mmarek@suse.cz> Link: http://lkml.kernel.org/r/1431951554-5563-3-git-send-email-hofrat@osadl.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'include/linux/jiffies.h')
-rw-r--r--include/linux/jiffies.h18
1 files changed, 15 insertions, 3 deletions
diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 9527ddbb0f1b..5e75af6cf1bc 100644
--- 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);