Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=8c660065383976f09fbdae86c33448c8da643d4e
Commit: 8c660065383976f09fbdae86c33448c8da643d4e
Parent: edaf420fdc122e7a42326fe39274c8b8c9b19d41
Author: Dave Johnson <[EMAIL PROTECTED]>
AuthorDate: Tue Oct 23 22:37:22 2007 +0200
Committer: Thomas Gleixner <[EMAIL PROTECTED]>
CommitDate: Tue Oct 23 22:37:22 2007 +0200
x86: fix more TSC clock source calibration errors
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 <[EMAIL PROTECTED]>
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
Signed-off-by: Thomas Gleixner <[EMAIL PROTECTED]>
---
arch/x86/kernel/tsc_32.c | 34 ++++++++++++++++++++--------------
1 files changed, 20 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
index f04d08a..9ebc0da 100644
--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -137,31 +137,37 @@ unsigned long native_calculate_cpu_khz(void)
local_irq_save(flags);
- /* run 3 times to ensure the cache is warm */
+ /* run 3 times to ensure the cache is warm and to get an accurate
reading */
for (i = 0; i < 3; i++) {
mach_prepare_counter();
rdtscll(start);
mach_countup(&count);
rdtscll(end);
+
+ /*
+ * Error: ECTCNEVERSET
+ * The CTC wasn't reliable: we got a hit on the very first read,
+ * or the CPU was so fast/slow that the quotient wouldn't fit in
+ * 32 bits..
+ */
+ if (count <= 1)
+ continue;
+
+ /* cpu freq too slow: */
+ if ((end - start) <= CALIBRATE_TIME_MSEC)
+ continue;
+
+ /*
+ * We want the minimum time of all runs in case one of them
+ * is inaccurate due to SMI or other delay
+ */
delta64 = min(delta64, (end - start));
}
- /*
- * Error: ECTCNEVERSET
- * The CTC wasn't reliable: we got a hit on the very first read,
- * or the CPU was so fast/slow that the quotient wouldn't fit in
- * 32 bits..
- */
- if (count <= 1)
- goto err;
- /* cpu freq too fast: */
+ /* cpu freq too fast (or every run was bad): */
if (delta64 > (1ULL<<32))
goto err;
- /* cpu freq too slow: */
- if (delta64 <= CALIBRATE_TIME_MSEC)
- goto err;
-
delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
do_div(delta64,CALIBRATE_TIME_MSEC);
-
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