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x86: warn of incorrect cpu_khz on AMD systems

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Impact: add debug check

If none of the perfctrs are free when calculating cpu_khz we default to
using ctr 3 (ie, we just choose 3).  This may lead to an incorrect tsc
freq value which can cause the system to be unstable.

To aid in future debugging, WARN the user of a potential problem.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Prarit Bhargava 2008-11-12 13:35:00 -05:00 committed by Ingo Molnar
parent 6cf87efbc7
commit 8652cb4b0d
1 changed files with 2 additions and 0 deletions
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2
arch/x86/kernel/time_64.c
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@ -80,6 +80,8 @@ unsigned long __init calibrate_cpu(void)
break; break;
no_ctr_free = (i == 4); no_ctr_free = (i == 4);
if (no_ctr_free) { if (no_ctr_free) {
WARN(1, KERN_WARNING "Warning: AMD perfctrs busy ... "
"cpu_khz value may be incorrect.\n");
i = 3; i = 3;
rdmsrl(MSR_K7_EVNTSEL3, evntsel3); rdmsrl(MSR_K7_EVNTSEL3, evntsel3);
wrmsrl(MSR_K7_EVNTSEL3, 0); wrmsrl(MSR_K7_EVNTSEL3, 0);