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[PATCH] x86_64: Make udelay more accurate

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The attempt to avoid overflow in __delay caused varying precision
on different CPUs depending on differences in the CPU speed.

We should be able to do this multiplication with out overflowing
provided the
cpu is running at less than about 128 GHz.  xloops < 20000 * 0x10c6.
loops_per_jiffy * HZ <= cpu_clock_speed.  So if the cpu clock speed
< 2^64/(20000 * 0x10c6) = 2^64/ 51E6CC0 < 2^64/2^27 = 2^37 = 128G we
will not overflow the calculation.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Ross Biro 2006-01-11 22:43:51 +01:00 committed by Linus Torvalds
parent e4e94072d9
commit 79c62cf178
1 changed files with 1 additions and 1 deletions
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2
arch/x86_64/lib/delay.c
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@ -39,7 +39,7 @@ void __delay(unsigned long loops)
inline void __const_udelay(unsigned long xloops)
{
__delay(((xloops * cpu_data[raw_smp_processor_id()].loops_per_jiffy) >> 32) * HZ);
__delay((xloops * HZ * cpu_data[raw_smp_processor_id()].loops_per_jiffy) >> 32);
}
void __udelay(unsigned long usecs)