Re: [gentoo-dev] Re: ICC Profile
Duncan wrote: Has anyone done a study of -Os vs -O2 with gcc-4.3.x, Just a quick note while on the subject : -Os is known to break some packages. Although it has been a while since I've last had a full -Os system, there was a time when -Os was a _very_bad_idea_. That's why the Gnome Herd (and upstream Gnome) won't support anything more than -O2. Of course, if anyone wants to use -Os to actually fix bugs... :) Cheers Rémi -- gentoo-dev@lists.gentoo.org mailing list
Re: [gentoo-dev] Re: ICC Profile
I actually know somebody working at intel, maybe he can get them more involved. -- gentoo-dev@lists.gentoo.org mailing list
Re: [gentoo-dev] Re: ICC Profile
BTW: Is ICC really worth the fuss ? I have checked around and reported that newest gcc-4.3 is able to to catch and sometimes even outperform icc ( not always, naturally). Big news seemed to be thatnew gcc si close and sometimes better than icc. Is it any truth to that and if it is, what is the motive of having non-open icc option ? Adam Stylinski wrote: I actually know somebody working at intel, maybe he can get them more involved. -- gentoo-dev@lists.gentoo.org mailing list
Re: [gentoo-dev] Re: ICC Profile
GCC 4.3 is catching up, but they are no where near utilizing SSE4 or SSE5 instructions. http://blog.alphagemini.org/2008/03/icc-vs-gcc-43.html He concludes that it's not worth pursuing, but I beg to differ. Those are signifcant differences for a processor. -- gentoo-dev@lists.gentoo.org mailing list
Re: [gentoo-dev] Re: ICC Profile
On Fri, 18 Jul 2008 10:24:58 -0400 (EDT) Adam Stylinski [EMAIL PROTECTED] wrote: GCC 4.3 is catching up, but they are no where near utilizing SSE4 or SSE5 instructions. http://blog.alphagemini.org/2008/03/icc-vs-gcc-43.html He concludes that it's not worth pursuing, but I beg to differ. Those are signifcant differences for a processor. He doesn't establish whether the code in question is highly cpu-bound or not when run on his system. For a lot of memory- and i/o-bound code, there's little practical difference between gcc with optimisations turned off and gcc with -frice-my-shorts except that the former compiles an order of magnitude faster. The more interesting question, then, is whether users run any non-trivial cpu-bound programs. We know the applied science types do, but they tend to be the ones who're doing clever things with icc anyway. What about normal users? -- Ciaran McCreesh signature.asc Description: PGP signature
Re: [gentoo-dev] Re: ICC Profile
He's also doing it on a core 2 duo. It would be interesting to compare this with some mildly legacy hardware (netburst pipelines) in order to see whether GCC does a comparable job. My guess would be no, seeing as netburst was extremely ugly and complicated, only intel would be able to write a compiler that took advantage of it. -- gentoo-dev@lists.gentoo.org mailing list
Re: [gentoo-dev] Re: ICC Profile
Ciaran McCreesh wrote: The more interesting question, then, is whether users run any non-trivial cpu-bound programs. We know the applied science types do, but they tend to be the ones who're doing clever things with icc anyway. What about normal users? I'm sure they do on some occasion if they encode compressed audio/video, or when compressing data with zip/etc. That is probably the biggest application of cpu-bound software. Personally, I use -Os across the board when it doesn't break. As you said I tend to be memory/IO bound, and optimizing for size helps with both (swapping causes IO). I'd probably benefit from using -O3 on the aforementioned CPU-intensive apps. -- gentoo-dev@lists.gentoo.org mailing list
Re: [gentoo-dev] Re: ICC Profile
On Fri, 18 Jul 2008 15:34:53 -0400 Richard Freeman [EMAIL PROTECTED] wrote: Ciaran McCreesh wrote: The more interesting question, then, is whether users run any non-trivial cpu-bound programs. We know the applied science types do, but they tend to be the ones who're doing clever things with icc anyway. What about normal users? I'm sure they do on some occasion if they encode compressed audio/video, or when compressing data with zip/etc. That is probably the biggest application of cpu-bound software. How much of that is memory bound? Of the things that aren't, how many aren't written in assembly anyway? Of those things, what proportion of the runtime is spent in those areas? If you double the speed of something that takes up 2% of the overall execution time, you can't measure the improvement. Or looking at it the other way -- is there any reason to believe that using icc (which can end up being a substantial pain in the arse, given the way it tries to use gcc's c++ headers but doesn't support some of the extensions or quirks that g++ does) will provide a genuine gain for people who aren't already doing clever profile-directed trickery anyway? I'd probably benefit from using -O3 on the aforementioned CPU-intensive apps. The problem with -O3 is that function inlining can lead to a substantial cache hit. Unless you're using profile-directed optimisations, which Gentoo doesn't support, it's extremely hit and miss as to whether O3 helps or hurts. -- Ciaran McCreesh signature.asc Description: PGP signature
Re: [gentoo-dev] Re: ICC Profile
Ciaran McCreesh wrote: How much of that is memory bound? Of the things that aren't, how many aren't written in assembly anyway? Of those things, what proportion of the runtime is spent in those areas? If you double the speed of something that takes up 2% of the overall execution time, you can't measure the improvement. Or looking at it the other way -- is there any reason to believe that using icc (which can end up being a substantial pain in the arse, given the way it tries to use gcc's c++ headers but doesn't support some of the extensions or quirks that g++ does) will provide a genuine gain for people who aren't already doing clever profile-directed trickery anyway? The problem with -O3 is that function inlining can lead to a substantial cache hit. Unless you're using profile-directed optimisations, which Gentoo doesn't support, it's extremely hit and miss as to whether O3 helps or hurts. I agree with all of the above. Gentoo is about choice, so if people want to make ICC work well more power to them. I agree that it would be hard to make it THE ONLY system compiler. For those who do try it I'd be really interested in their findings. -- gentoo-dev@lists.gentoo.org mailing list
Re: [gentoo-dev] Re: ICC Profile
Perhaps we could write a script that compiles packages in portage with both ICC and GCC and runs them with different flags. I think there was an effort on the GCC side already to test flags with specific packages. We can then have the script run time on the applications doing work (again, that's a lot of packages for a lot of different tasks). If we can store these in the portage tree (yes, it's more metadata), the user can actually benefit well from the optimizations. -- gentoo-dev@lists.gentoo.org mailing list
