Commit e10f7805 authored Jul 14, 2018 by Peng Hao Committed by Paolo Bonzini Jul 18, 2018

kvmclock: fix TSC calibration for nested guests



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>

parent 2307af1c

arch/x86/kernel/kvmclock.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}