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
..
alpha	alpha: sg_virt() fallout	2007-10-23 12:31:05 +02:00
arm	arm: build fix	2007-10-23 09:11:41 +02:00
avr32	[AVR32] ARRAY_SIZE() cleanup	2007-10-23 11:20:26 +02:00
blackfin	Merge branch 'for-linus' of master.kernel.org:/pub/scm/linux/kernel/git/cooloney/blackfin-2.6	2007-10-22 19:29:05 -07:00
cris	typo fixes	2007-10-20 01:34:40 +02:00
frv	spelling fixes: arch/frv/	2007-10-20 01:09:42 +02:00
h8300	spelling fixes: arch/h8300/	2007-10-20 01:10:46 +02:00
i386	x86: add instrumentation menu	2007-10-23 22:37:22 +02:00
ia64	Merge branch 'sg' of git://git.kernel.dk/linux-2.6-block	2007-10-22 19:11:06 -07:00
m32r	spelling fixes: arch/m32r/	2007-10-20 01:14:39 +02:00
m68k	Update arch/ to use sg helpers	2007-10-22 21:19:59 +02:00
m68knommu	m68knommu: cleanup m68knommu timer code	2007-10-23 08:32:35 -07:00
mips	mips: sg_page() fallout	2007-10-23 12:32:34 +02:00
parisc	parisc: fix sg_page() fallout	2007-10-23 09:49:31 +02:00
powerpc	Merge branch 'for-2.6.24' of master.kernel.org:/pub/scm/linux/kernel/git/jwboyer/powerpc-4xx into merge	2007-10-23 22:20:51 +10:00
ppc	kbuild: restore arch/{ppc/xtensa}/boot cflags	2007-10-20 20:35:23 +02:00
s390	[S390] 4level-fixup cleanup	2007-10-22 12:52:49 +02:00
sh	Combine instrumentation menus in kernel/Kconfig.instrumentation	2007-10-19 11:53:54 -07:00
sh64	Fix misspellings of "system", "controller", "interrupt" and "necessary".	2007-10-19 23:10:43 +02:00
sparc	Update arch/ to use sg helpers	2007-10-22 21:19:59 +02:00
sparc64	sparc64: zero out dma_length	2007-10-23 12:58:39 +02:00
um	[SG] Update drivers to use sg helpers	2007-10-22 21:19:53 +02:00
v850	spelling fixes: arch/v850/	2007-10-20 01:24:05 +02:00
x86	x86: fix TSC clock source calibration error	2007-10-23 22:37:22 +02:00
x86_64	x86: add instrumentation menu	2007-10-23 22:37:22 +02:00
xtensa	kbuild: restore arch/{ppc/xtensa}/boot cflags	2007-10-20 20:35:23 +02:00