Dave Johnson edaf420fdc x86: fix TSC clock source calibration error ... I ran into this problem on a system that was unable to obtain NTP sync because the clock was running very slow (over 10000ppm slow). ntpd had declared all of its peers 'reject' with 'peer_dist' reason. On investigation, the tsc_khz variable was significantly incorrect causing xtime to run slow. After a reboot tsc_khz was correct so I did a reboot test to see how often the problem occurred: Test was done on a 2000 Mhz Xeon system. Of 689 reboots, 8 of them had unacceptable tsc_khz values (>500ppm): range of tsc_khz # of boots % of boots ---------------- ---------- ---------- < 1999750 0 0.000% 1999750 - 1999800 21 3.048% 1999800 - 1999850 166 24.128% 1999850 - 1999900 241 35.029% 1999900 - 1999950 211 30.669% 1999950 - 2000000 42 6.105% 2000000 - 2000000 0 0.000% 2000050 - 2000100 0 0.000% [...] 2000100 - 2015000 1 0.145% << BAD 2015000 - 2030000 6 0.872% << BAD 2030000 - 2045000 1 0.145% << BAD 2045000 < 0 0.000% The worst boot was 2032.577 Mhz, over 1.5% off! It appears that on rare occasions, mach_countup() is taking longer to complete than necessary. I suspect that this is caused by the CPU taking a periodic SMI interrupt right at the end of the 30ms calibration loop. This would cause the loop to delay while the SMI BIOS hander runs. The resulting TSC value is beyond what it actually should be resulting in a higher tsc_khz. The below patch makes native_calculate_cpu_khz() take the best (shortest duration, lowest khz) run of it's 3 calibration loops. If a SMI goes off causing a bad result (long duration, higher khz) it will be discarded. With the patch applied, 300 boots of the same system produce good results: range of tsc_khz # of boots % of boots ---------------- ---------- ---------- < 1999750 0 0.000% 1999750 - 1999800 30 10.000% 1999800 - 1999850 166 55.333% 1999850 - 1999900 89 29.667% 1999900 - 1999950 15 5.000% 1999950 < 0 0.000% Problem was found and tested against 2.6.18. Patch is against 2.6.22. Signed-off-by: Dave Johnson <djohnson@sw.starentnetworks.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>		2007-10-23 22:37:22 +02:00
..
boot	i386: paravirt boot sequence	2007-10-22 08:13:17 -07:00
crypto	x86_64: move crypto	2007-10-11 11:17:03 +02:00
ia32	x86: Use linux/elfcore-compat.h	2007-10-19 20:35:02 +02:00
kernel	x86: fix TSC clock source calibration error	2007-10-23 22:37:22 +02:00
lguest	Revert lguest magic and use hook in head.S	2007-10-23 15:49:57 +10:00
lib	Merge ssh://master.kernel.org/pub/scm/linux/kernel/git/tglx/linux-2.6-x86	2007-10-19 15:06:00 -07:00
mach-default	spelling fixes: arch/i386/	2007-10-20 01:13:56 +02:00
mach-es7000	i386: es7000 minor cleanups	2007-10-17 20:16:15 +02:00
mach-generic	spelling fixes: arch/i386/	2007-10-20 01:13:56 +02:00
mach-visws	[x86] remove uses of magic macros for boot_params access	2007-10-16 17:38:31 -07:00
mach-voyager	Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial	2007-10-19 20:36:17 -07:00
math-emu	kbuild: fix up CFLAGS usage	2007-10-14 21:49:42 +02:00
mm	Intel IOMMU: clflush_cache_range now takes size param	2007-10-22 08:13:18 -07:00
oprofile	x86: add instrumentation menu	2007-10-23 22:37:22 +02:00
pci	spelling fixes: arch/i386/	2007-10-20 01:13:56 +02:00
power	i386: move power	2007-10-11 11:16:34 +02:00
vdso	x86: vdso linker script cleanup	2007-10-17 20:17:06 +02:00
video	i386: move video	2007-10-11 11:16:56 +02:00
xen	Normalize config options for guest support	2007-10-23 15:49:47 +10:00