Re: performance counter ~0.4% error finding retired instructioncount

[Paul Mackerras]

Ingo Molnar writes:

> I measured 2000, but generally a few thousand cycles per invocation 
> sounds about right.

We could actually do a bit better than we do, fairly easily.  We could
attach the counters to the child after the fork instead of the parent
before the fork, using a couple of pipes for synchronization.  And
there's probably a way to get the dynamic linker to resolve the execvp
call early in the child so we avoid that overhead.  I think we should
be able to get the overhead down to tens of userspace instructions
without doing anything unnatural.

Paul.
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