incoming QPI traffic on Haswell

[abasak24]

Hi,
It looks like QPIIncomingTraffic is not available on Haswell Architecture. Could you please explain why?

bool incomingQPITrafficMetricsAvailable() const
{
return getQPILinksPerSocket() > 0 &&
(
cpu_model == PCM::NEHALEM_EX
|| cpu_model == PCM::WESTMERE_EX
|| cpu_model == PCM::JAKETOWN
|| cpu_model == PCM::IVYTOWN
|| (cpu_model == PCM::SKX && cpu_stepping > 1)
);
}

[opcm]

This metric was over counting on Haswell and Broadwell therefore it has been disabled.

[abasak24]

got it, thanks for your response!

[ogbrugge]

Should we add a comment here stating the finding that the counter is overcounting? This will prevent future questions.

[ogbrugge]

I also mean this in general, whenever a cpu model is left out of a list I think it should require a comment as to why it was left out.

[soramichi]

Can you please point a document that explains this phenomenon?

I once observed this (like 16 MB of QPI IO even when nothing interesting is going on), but at that time I though this traffic was to maintain the cache coherence and I didn't know that it was due to overcountng (bug)?