Re: GCC performance regression - up to 20% ?

[law@redhat.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