Re: [PATCH v2 6/4] selftests: kvm: Add basic Hyper-V clocksources tests

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 18/03/21 15:09, Vitaly Kuznetsov wrote:
>> +static inline void check_tsc_msr_tsc_page(struct ms_hyperv_tsc_page *tsc_page)
>> +{
>> +	u64 r1, r2, t1, t2;
>> +	s64 delta_ns;
>> +
>> +	/* Compare TSC page clocksource with HV_X64_MSR_TIME_REF_COUNT */
>> +	t1 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + tsc_page->tsc_offset;
>> +	r1 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
>> +	nop_loop();
>> +	t2 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + tsc_page->tsc_offset;
>> +	r2 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
>> +
>> +	delta_ns = ((r2 - r1) - (t2 - t1)) * 100;
>> +	if (delta_ns < 0)
>> +		delta_ns = -delta_ns;
>> +
>> +	/* 1% tolerance */
>> +	GUEST_ASSERT(delta_ns * 100 < (t2 - t1) * 100);
>> +}
>> +
>
> I think you should also be able to check r1 and r2 individually, not 
> just r1 and r2.  Is that correct?

Right, we could've checked r1 == t1 and r2 == t2 actually (with some
tiny margin of course). Let me try that.

-- 
Vitaly