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Re: GCC performance regression - up to 20% ?
- From: law at redhat dot com
- To: Carlo Wood <carlo at alinoe dot com>
- Cc: Michel LESPINASSE <walken at zoy dot org>, Jan Hubicka <jh at suse dot cz>, Andreas Jaeger <aj at suse dot de>, gcc list <gcc at gcc dot gnu dot org>
- Date: Mon, 22 Apr 2002 08:24:25 -0600
- Subject: Re: GCC performance regression - up to 20% ?
- Reply-to: law at redhat dot com
In message <20020422155801.A21747@alinoe.com>, Carlo Wood writes:
> >
> > Then I tried to figure out where the slowdown is, using gprof. And
> > this is where things get really interesting: gprof tells me that the
> > code compiled with 3.1 is faster, but 'time' tells me that the user
> > time spent executing that code is higher with 3.1 than with 2.95. I'm
> > not sure what to make of this, but I think this might give you some
> > clues, so I'll describe it in more detail. I'm not sure what the
> > overhead is, but it seems to be right in gprof's blind spot.
>
> gprof "measures" the time that a function takes by probing
> which function the program is executing about every 20 ms.
> >From that it builds up a statistical histogram.
>
> I wish there would be a more precise profiler that uses the
> hardware counters. Does anyone know of one? Hmm, I remember
> a Subject: line on the PAPI mailinglist that mentioned gprof,
> but I deleted it. I think it asked the same question: whether
> or not there existed a 'gprof' that used PAPI.
You might look at oprofile.
jeff