Very sporadically hitting recently-added assert in PresentMonTraceConsumer.cpp

[austinkinross]

Hi! I'm from the PIX on Windows team. A few weeks ago we updated PIX to use the top-of-tree PresentMon. Since then, it's been running in our test lab nightly, and one of our test runs recently hit this assert:

https://github.com/GameTechDev/PresentMon/blob/6320933cfaa373cb1702126c0449cf28b9c3431f/PresentData/PresentMonTraceConsumer.cpp#L349

Unfortunately, I don't have any repro steps. Our nightly tests have hit this once in approximately 5,000 PresentMon sessions that our tests have created since we updated PresentMon.

From the crash dump, presentsBySubmitSequence had one entry for the hContext:

Which is completely different to the value of "present":

We (PIX) use our own ETW infrastructure to create ETW sessions and pass the raw events to PresentMon code, but otherwise the PresentMon code is unchanged. Perhaps PIX isn't enabling all of the right ETW events? Or perhaps PresentMon has a bug?

I'm wondering if you have any insight into what might be causing this? Thank you!