mesa-users] weird performance collapse for mesa with gfortran on mac

Bill Paxton paxton at
Wed Sep 29 12:18:41 EDT 2010

Just for a change, I'll ask a question on mesa-users rather than try to give an answer.

I've run into a mystery with gfortran on my mac.  My usual compiler is ifort,
but once in a while I run something using gfortran just to check.  Up until recently
there was a small difference in performance -- gfortran was perhaps 25% slower
on average.   But yesterday, I ran a small test, and the runtime for gfortran mesa
was bizarre -- more than 20 times slower!   I checked the Activity Monitor and
discovered that with gfortran, mesa was spending almost all of its time in system
calls -- whereas with ifort and in the old days with gfortran the system time is tiny.

This is a mac problem -- I did the same comparision of ifort and gfortran on a linux
machine and found only a small difference in performance (same as I used to 
see on the mac).

I'm running the gfortran 4.5.1 release, and I upgraded to Xcode 3.2.3 recently.
Perhaps the new Xcode is the problem?

If anyone has seen a similar degradation in performance, I'd like to know.
And if you've figured out a solution, I'd really like to know.

If you are a student and run into this, you might want to switch to ifort.
Intel offers a "Intel® Software Development Suite Student Edition for Mac OS"
for only $49 -- it includes ifort.


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