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author | Eric Dumazet <dada1@cosmosbay.com> | 2007-05-08 07:25:32 (GMT) |
---|---|---|
committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-05-08 18:15:01 (GMT) |
commit | 753e9c5cd9b123156152c66c816f751954b15e53 (patch) | |
tree | fc70e4358be312e11ce0c258ead7b996dbd7d59e /kernel | |
parent | 2e17c5508fa015f2c7690e29041f437e9308c64f (diff) | |
download | linux-fsl-qoriq-753e9c5cd9b123156152c66c816f751954b15e53.tar.xz |
Optimize timespec_trunc()
The first thing done by timespec_trunc() is :
if (gran <= jiffies_to_usecs(1) * 1000)
This should really be a test against a constant known at compile time.
Alas, it isnt. jiffies_to_usec() was unilined so C compiler emits a function
call and a multiply to compute : a CONSTANT.
mov $0x1,%edi
mov %rbx,0xffffffffffffffe8(%rbp)
mov %r12,0xfffffffffffffff0(%rbp)
mov %edx,%ebx
mov %rsi,0xffffffffffffffc8(%rbp)
mov %rsi,%r12
callq ffffffff80232010 <jiffies_to_usecs>
imul $0x3e8,%eax,%eax
cmp %ebx,%eax
This patch reorders kernel/time.c a bit so that jiffies_to_usecs() is defined
before timespec_trunc() so that compiler now generates :
cmp $0x3d0900,%edx (HZ=250 on my machine)
This gives a better code (timespec_trunc() becoming a leaf function), and
shorter kernel size as well.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/time.c | 60 |
1 files changed, 30 insertions, 30 deletions
diff --git a/kernel/time.c b/kernel/time.c index ba18ec4..6d98ab7 100644 --- a/kernel/time.c +++ b/kernel/time.c @@ -247,6 +247,36 @@ struct timespec current_fs_time(struct super_block *sb) } EXPORT_SYMBOL(current_fs_time); +/* + * Convert jiffies to milliseconds and back. + * + * Avoid unnecessary multiplications/divisions in the + * two most common HZ cases: + */ +unsigned int inline jiffies_to_msecs(const unsigned long j) +{ +#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) + return (MSEC_PER_SEC / HZ) * j; +#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) + return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); +#else + return (j * MSEC_PER_SEC) / HZ; +#endif +} +EXPORT_SYMBOL(jiffies_to_msecs); + +unsigned int inline jiffies_to_usecs(const unsigned long j) +{ +#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) + return (USEC_PER_SEC / HZ) * j; +#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) + return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC); +#else + return (j * USEC_PER_SEC) / HZ; +#endif +} +EXPORT_SYMBOL(jiffies_to_usecs); + /** * timespec_trunc - Truncate timespec to a granularity * @t: Timespec @@ -473,36 +503,6 @@ struct timeval ns_to_timeval(const s64 nsec) EXPORT_SYMBOL(ns_to_timeval); /* - * Convert jiffies to milliseconds and back. - * - * Avoid unnecessary multiplications/divisions in the - * two most common HZ cases: - */ -unsigned int jiffies_to_msecs(const unsigned long j) -{ -#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) - return (MSEC_PER_SEC / HZ) * j; -#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) - return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); -#else - return (j * MSEC_PER_SEC) / HZ; -#endif -} -EXPORT_SYMBOL(jiffies_to_msecs); - -unsigned int jiffies_to_usecs(const unsigned long j) -{ -#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) - return (USEC_PER_SEC / HZ) * j; -#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) - return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC); -#else - return (j * USEC_PER_SEC) / HZ; -#endif -} -EXPORT_SYMBOL(jiffies_to_usecs); - -/* * When we convert to jiffies then we interpret incoming values * the following way: * |