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kvmclock: fix TSC calibration for nested guests

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Inside a nested guest, access to hardware can be slow enough that
tsc_read_refs always return ULLONG_MAX, causing tsc_refine_calibration_work
to be called periodically and the nested guest to spend a lot of time
reading the ACPI timer.

However, if the TSC frequency is available from the pvclock page,
we can just set X86_FEATURE_TSC_KNOWN_FREQ and avoid the recalibration.
'refine' operation.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
[Commit message rewritten. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Peng Hao 2018-07-14 23:28:29 +08:00 committed by Paolo Bonzini
parent 2307af1c4b
commit e10f780503
1 changed files with 1 additions and 0 deletions
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arch/x86/kernel/kvmclock.c
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@ -138,6 +138,7 @@ static unsigned long kvm_get_tsc_khz(void)
src = &hv_clock[cpu].pvti;
tsc_khz = pvclock_tsc_khz(src);
put_cpu();
setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
return tsc_khz;
}