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KVM: selftests: Make hyperv_clock selftest more stable 

hyperv_clock doesn't always give a stable test result, especially with
AMD CPUs. The test compares Hyper-V MSR clocksource (acquired either
with rdmsr() from within the guest or KVM_GET_MSRS from the host)
against rdtsc(). To increase the accuracy, increase the measured delay
(done with nop loop) by two orders of magnitude and take the mean rdtsc()
value before and after rdmsr()/KVM_GET_MSRS.

Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Tested-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220601144322.1968742-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2022-06-01 16:43:22 +02:00 committed by Paolo Bonzini
parent 5ba7c4c6d1
commit eae260be3a
1 changed files with 7 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
tools/testing/selftests/kvm/x86_64/hyperv_clock.c
View File

@ -44,7 +44,7 @@ static inline void nop_loop(void)
{
int i;
for (i = 0; i < 1000000; i++)
for (i = 0; i < 100000000; i++)
asm volatile("nop");
}
@ -56,12 +56,14 @@ static inline void check_tsc_msr_rdtsc(void)
tsc_freq = rdmsr(HV_X64_MSR_TSC_FREQUENCY);
GUEST_ASSERT(tsc_freq > 0);
/* First, check MSR-based clocksource */
/* For increased accuracy, take mean rdtsc() before and afrer rdmsr() */
r1 = rdtsc();
t1 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
r1 = (r1 + rdtsc()) / 2;
nop_loop();
r2 = rdtsc();
t2 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
r2 = (r2 + rdtsc()) / 2;
GUEST_ASSERT(r2 > r1 && t2 > t1);
@ -181,12 +183,14 @@ static void host_check_tsc_msr_rdtsc(struct kvm_vm *vm)
tsc_freq = vcpu_get_msr(vm, VCPU_ID, HV_X64_MSR_TSC_FREQUENCY);
TEST_ASSERT(tsc_freq > 0, "TSC frequency must be nonzero");
/* First, check MSR-based clocksource */
/* For increased accuracy, take mean rdtsc() before and afrer ioctl */
r1 = rdtsc();
t1 = vcpu_get_msr(vm, VCPU_ID, HV_X64_MSR_TIME_REF_COUNT);
r1 = (r1 + rdtsc()) / 2;
nop_loop();
r2 = rdtsc();
t2 = vcpu_get_msr(vm, VCPU_ID, HV_X64_MSR_TIME_REF_COUNT);
r2 = (r2 + rdtsc()) / 2;
TEST_ASSERT(t2 > t1, "Time reference MSR is not monotonic (%ld <= %ld)", t1, t2);