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

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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?

Paolo




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