PGI User Forum

deeppow · Joined: 02 Feb 2012 Posts: 51

Matt,

"-Munrol=n:4" gave me an ~15% speed up on my test problem, from ~10min to ~8.5min. There was more than just the one case I noted.

This situation arises due to my use of indirect addressing (what you call table lookup) for array indexes for a large number of cases (mesh/grid cells).

-ralph

mkcolg · Posted: Fri Mar 08, 2013 4:16 pm Post subject:

Any benefit if you increase the unroll factor even further? -Munroll=n:8 or even -Munroll=n:64?

- Mat

deeppow · Joined: 02 Feb 2012 Posts: 51

No improvement. I tried 8. I did look at the task manager cpu loading with 4 and it was at or near 100% most of the time so I figured it wasn't going to help much.

I understand what the unrolling does to the do-loop but I'm not quite sure how it uses the cpu architecture. Would assume the unrolled loops are shipped off to different cores. How is this different than parallelization regarding a cpu?

mkcolg · Posted: Mon Mar 11, 2013 9:09 am Post subject:

deeppow · Joined: 02 Feb 2012 Posts: 51

Matt,
I must show my ignorance here. I would interpret sequential to mean on only 1 core, i.e. just like an old single-core scaler processor. If that is true of what advantage is unrolling? Would seem to even add a little loop overhead. Since that makes no sense, I conclude I have something wrong in my thinking.

-ralph