The previous patch wasn't correctly handling the 'count' variable. If
a CPU gave bad results on the 1st or 2nd run but good results on the
3rd, it wouldn't do the correct thing. No idea if any such CPU
exists, but the patch below handles that case by discarding the bad
runs.
If a bad result (too quick, or too slow) occurs on any of the 3 runs
it will be discarded.
Also updated some comments to explain what's going on.
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>
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>
* git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial: (74 commits)
fix do_sys_open() prototype
sysfs: trivial: fix sysfs_create_file kerneldoc spelling mistake
Documentation: Fix typo in SubmitChecklist.
Typo: depricated -> deprecated
Add missing profile=kvm option to Documentation/kernel-parameters.txt
fix typo about TBI in e1000 comment
proc.txt: Add /proc/stat field
small documentation fixes
Fix compiler warning in smount example program from sharedsubtree.txt
docs/sysfs: add missing word to sysfs attribute explanation
documentation/ext3: grammar fixes
Documentation/java.txt: typo and grammar fixes
Documentation/filesystems/vfs.txt: typo fix
include/asm-*/system.h: remove unused set_rmb(), set_wmb() macros
trivial copy_data_pages() tidy up
Fix typo in arch/x86/kernel/tsc_32.c
file link fix for Pegasus USB net driver help
remove unused return within void return function
Typo fixes retrun -> return
x86 hpet.h: remove broken links
...
cpu_data is currently an array defined using NR_CPUS. This means that
we overallocate since we will rarely really use maximum configured cpus.
When NR_CPU count is raised to 4096 the size of cpu_data becomes
3,145,728 bytes.
These changes were adopted from the sparc64 (and ia64) code. An
additional field was added to cpuinfo_x86 to be a non-ambiguous cpu
index. This corresponds to the index into a cpumask_t as well as the
per_cpu index. It's used in various places like show_cpuinfo().
cpu_data is defined to be the boot_cpu_data structure for the NON-SMP
case.
Signed-off-by: Mike Travis <travis@sgi.com>
Acked-by: Christoph Lameter <clameter@sgi.com>
Cc: Andi Kleen <ak@suse.de>
Cc: James Bottomley <James.Bottomley@steeleye.com>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Mark M. Hoffman <mhoffman@lightlink.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Since the x86 merge, lots of files that referenced their own filenames
are no longer correct. Rather than keep them up to date, just delete
them, as they add no real value.
Additionally:
- fix up comment formatting in scx200_32.c
- Remove a credit from myself in setup_64.c from a time when we had no SCM
- remove longwinded history from tsc_32.c which can be figured out from
git.
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
