Commit-ID: c569a23d65ac2900d9998d3fe04044fe95be6b2f
Gitweb: http://git.kernel.org/tip/c569a23d65ac2900d9998d3fe04044fe95be6b2f
Author: Nicholas Mc Guire <hofrat@xxxxxxxxx>
AuthorDate: Thu, 28 May 2015 19:09:56 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 10 Jun 2015 11:31:14 +0200
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@xxxxxxxxx>
Cc: Masahiro Yamada <yamada.m@xxxxxxxxxxxxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Andrew Hunter <ahh@xxxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Michal Marek <mmarek@xxxxxxx>
Link: http://lkml.kernel.org/r/1432832996-12129-2-git-send-email-hofrat@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
include/linux/jiffies.h | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index a316ebe..535fd3b 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);
--
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