having two compilers is good

Posted Feb 28, 2009 18:18 UTC (Sat) by Trelane (subscriber, #56877)
In reply to: having two compilers is good by joib
Parent article: LinuxDNA Supercharges Linux with the Intel C/C++ Compiler (Linux Journal)

might also check out the profiling support in gcc (compile with profiling, run the program in a hopefully representative way, and then re-compile based upon the profiling information), and some things like dropping frame pointers. Oh, and -mfpmath=sse and -march=native (in latest stable gcc; you might need to actually specify your arch if you're on an earlier version)

Have you benchmarked on atom? I'd be interested in that; I've not benchmarked on atom yet. I can tell you for certain that the speed difference on a sample piece of code I ran (I think it was relaxation to solve electric potential) saw a significant boost when compiled with intel's compiler vs gcc on ia64.

I'd expect atom's performance to be sensitive to scheduling, due to the in-order execution. You might overcome some of the limitations by explicitly marking hot and cold sections (latest stable gcc) and especially by marking probable/improbable branches (likely/unlikely attributes in gcc 4 and later (?))

having two compilers is good

Posted Feb 28, 2009 18:19 UTC (Sat) by Trelane (subscriber, #56877) [Link]

oh, you already have native and sse, nm. ;) Couldn't see your post while writing. Sorry.

having two compilers is good

Posted Mar 1, 2009 0:21 UTC (Sun) by joib (subscriber, #8541) [Link] (1 responses)

No, I haven't tested atom. There are a few people working on atom specific optimization for the gcc backend, see

http://gcc.gnu.org/ml/gcc-patches/2009-01/msg00923.html

These improvements will likely make it into 4.5, maybe a year or so from now. I agree that as atom is in-order it's more sensitive to compiler scheduling. Perhaps that will widen the gap between gcc and the Intel compilers, I don't know.

As for IA-64, that is such an oddball architecture with a very small user base that it's not exactly surprising that gcc developers haven't spent that much time on it. Intel obviously has the motivation to make IA-64 look good compared to other architectures.

having two compilers is good

Posted Mar 1, 2009 4:17 UTC (Sun) by Trelane (subscriber, #56877) [Link]

Looking forward to seeing those patches land. I use atom on my main laptop (eee 901), and I'd love to have good performance on it. I wonder how it fares in flops/watt and flops/USD to other chips. If it's good, I might have money for an atom cluster in a few years.