Questions about Profile-guided Optimization

[jerryleo]

Hi,

I'd like to use the prof_gen with a Makefile for science computing optimization using MPI. The CPU is Xeon X7560.

My questions are

1. I wonder which one is more better, only using -O2 with prof-gen or more optimization options can be used at the same time

a. -O2 -prof-gen -prof-dir/$HOME/profiled
b. -w -O2 -xsse4.2 -xhost -prof-gen -prof-dir/$HOME/profiled
c. -w -O3 -xsse4.2 -xhost -prof-gen -prof-dir/$HOME/profiled

2. When I use -ipo with -prof-use, it always complains unsolved xxxx or undefined reference. But If I use -ip, it works fine with -prof-use. What's the problem?

3. Are there any more optimization options available for Xeon CPU for the science computing using MPI?

Thanks

Jerry