Commit 79c62cf1 authored by Ross Biro's avatar Ross Biro Committed by Linus Torvalds
Browse files

[PATCH] x86_64: Make udelay more accurate



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: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e4e94072
......@@ -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)
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment