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author | Nicholas Mc Guire <hofrat@osadl.org> | 2015-05-28 19:09:56 +0200 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2015-06-10 11:31:14 +0200 |
commit | c569a23d65ac2900d9998d3fe04044fe95be6b2f (patch) | |
tree | ecc4e449ec0918189cc6b78855980636069417f7 /include/linux/jiffies.h | |
parent | ae60d6a0e3a9197d37f8c8c4584a8ecd18518cd6 (diff) | |
download | lwn-c569a23d65ac2900d9998d3fe04044fe95be6b2f.tar.gz lwn-c569a23d65ac2900d9998d3fe04044fe95be6b2f.zip |
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.h | 30 |
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); |