Re: [PATCH] perf x86: Change SandyBridge and IvyBrige instructionsevent to be precise

From: Andi Kleen
Date: Wed Feb 20 2013 - 16:55:47 EST

> I don't think it buys you much. People read too much into what
> PEBS gives you. I can show you examples where PEBS
> is worse than no PEBS.

Nothing is perfect in sampling, but the precise instructions event
is definitely better in a range of situations. It avoids
a lot of shadow effects.

I think it's a good choice for a lot of situations, although
on Ivy Bridge without EventingRip the BB walking is still
fairly expensive.

It would be a good default for the "user only asks for instructions
for sampling and nothing else" situation, especially on Haswell
which has EventingRip. But that's not straight forward to detect.


ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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