Re: [patch] Performance Counters for Linux, v4

[Paul Mackerras]

Vince Weaver writes:

> I see a large (2300 instruction) fixed overhead when measuring
> retired instruction count using the "timec" command
> compared to the "pfmon" tool that comes with perfmon3
> (the pfmon tool has essentially no overhead when
> doing aggragate counts).

Looks like timec will be counting the fork() and execvp() system calls
that are used to run your executable, as well as the executable
itself.  The fork() overhead could be removed fairly easily I think,
the execvp would be hard to get rid of without using ptrace() - and
the use of ptrace was one of the things that Ingo et al. objected to
in perfmon3.

Paul.
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