On 18/03/21 17:57, Marcelo Tosatti wrote:
I think this should be monotonically increasing:
1. r1 = rdtsc();
2. t1 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
3. nop_loop();
4. r2 = rdtsc();
5. t2 = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
+ /* 1% tolerance */
+ GUEST_ASSERT(delta_ns * 100 < (t2 - t1) * 100);
+}
Doesnt an unbounded schedule-out/schedule-in (which resembles
overloaded host) of the qemu-kvm vcpu in any of the
points 1,2,3,4,5 break the assertion above?
Yes, there's a window of a handful of instructions (at least on
non-preemptible kernels). If anyone ever hits it, we can run the test
100 times and check that it passes at least 95 or 99 of them.
Paolo
