profile directed feedback.

girish vaitheeswaran
Tue Jul 12 20:29:00 GMT 2005

Has anyone gotten performance gains on account of
profile directed feedback optimization. I used
gcc-3.4.3 and tried using profile directed feedback.
This is what I did

1. Compiled the program using -fprofile-generate. I
used this flag both in the compile flags and as part
of the link flags. I also had to use libgcov.a during
the link phase otherwise it would die looking for gcov
2. Ran a representative work-load
3. Followed (1) except that instead of
-fprofile-generate used -fprofile-use

I had to drop the "-fprofile-use" on 2 files as they
had corrupted profile data. So far so good.

When I ran the profile directed feedback optimized
executable, the performance was 20% slower.

Anyone has experience with PDF they can share and
point out what I am doing wrong?


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