Comment by adsharma

Important distinction yes. It also means I can't go back and check the thread on what was said and when. Nor do I want to.

Always good to talk face to face if you're have strong feelings about something. When I said "talk" I meant literally face to face.

Spending a decade or so on lkml, everyone develops a thick skin. But mix it with the corporate environment, Facebook 2011, being an ex-employee adds more to the drama.

Having read through the comments here, I'm still of the opinion that any HW changes had a secondary effect and the primary contributor was a change in how HHVM/jemalloc interacted with MADV.

One more suggestion: evaluate more than one app and company wide profiling data to make such decisions.

One of the challenges in doing so is the large contingent of people who don't have an understanding of CPU uarch/counters and yet have a negative opinion of their usefulness to make decisions like this.

So the only tool you have left with is to run large scale rack level tests in a close to prod env, which has its own set of problems and benefits.