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authorNicholas Mc Guire <hofrat@osadl.org>2015-05-28 20:09:56 +0300
committerThomas Gleixner <tglx@linutronix.de>2015-06-10 12:31:14 +0300
commitc569a23d65ac2900d9998d3fe04044fe95be6b2f (patch)
treeecc4e449ec0918189cc6b78855980636069417f7 /include/linux/jiffies.h
parentae60d6a0e3a9197d37f8c8c4584a8ecd18518cd6 (diff)
downloadlinux-c569a23d65ac2900d9998d3fe04044fe95be6b2f.tar.xz
time: Allow gcc to fold usecs_to_jiffies(constant)
To allow constant folding in usecs_to_jiffies() conditionally calls the HZ dependent _usecs_to_jiffies() helpers or, when gcc can not figure out constant folding, __usecs_to_jiffies, which is the renamed original usecs_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/1432832996-12129-2-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.h30
1 files changed, 29 insertions, 1 deletions
diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index a316ebea0a89..535fd3bb1ba8 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -383,9 +383,37 @@ static inline unsigned long _usecs_to_jiffies(const unsigned int u)
}
#endif
+/**
+ * usecs_to_jiffies: - convert microseconds to jiffies
+ * @u: time in microseconds
+ *
+ * conversion is done as follows:
+ *
+ * - 'too large' values [that would result in larger than
+ * MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
+ *
+ * - all other values are converted to jiffies by either multiplying
+ * the input value by a factor or dividing it with a factor and
+ * handling any 32-bit overflows as for msecs_to_jiffies.
+ *
+ * usecs_to_jiffies() checks for the passed in value being a constant
+ * via __builtin_constant_p() allowing gcc to eliminate most of the
+ * code, __usecs_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 _usecs_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 usecs_to_jiffies(const unsigned int u)
{
- return __usecs_to_jiffies(u);
+ if (__builtin_constant_p(u)) {
+ if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
+ return MAX_JIFFY_OFFSET;
+ return _usecs_to_jiffies(u);
+ } else {
+ return __usecs_to_jiffies(u);
+ }
}
extern unsigned long timespec_to_jiffies(const struct timespec *value);