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Sorry for butchering your email, I only wanted to ask the list about one |
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point I saw that you made. |
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----- Original Message ----- |
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From: "William Kenworthy" <billk@×××××××××.au> |
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Subject: Re: [gentoo-dev] "Distro Day (Measuring the benefits of the |
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Gentooapproach)" |
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<snip> |
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> Wish more would do as you have done - I dont think too many follow this |
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> approach. Most seem to just do the reccomended, or go for the max. I |
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> did a few key apps, made my choices and have stayed with them. If a |
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> really useful cflags project gets up, it would be nice to run it |
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> regularly and perhaps find that the new gcc just emerged gives a |
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> measured 5% speed up if you use the new -supercharger flag! |
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I think that this is where the confusion with many "experts" on optimization |
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lies. What is a good program to use as a benchmark for optimizations and |
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compiler flags? How does one measure the performance gain? Is the |
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performance gain just in load time, or in processor usage throughout the |
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program? Do the benefits of using a particular optimization translate from |
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one program to the next? Some programs are snappier with -O2, some perform |
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twice as quick with -O3. Who is to say? How does one know for certain? |
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I have found that, for the most part, -O2 compiled apps runs much faster on |
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my system. I don't have any hard numbers, but I do know I decided to rebuild |
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my system recently with just -O2 ,-pipe, and -fomit-frame-pointer only - |
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Everything I do seems to be a bit more responsive. |
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>From what I've been hearing, I think the general consensus is that -O2 seems |
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to be a better optimization than -O3 *in general, for the most people*, yes? |
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Right now the "Decent examples" in make.conf include (in both examples) -O3 |
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as the optimization level to use. If -O2 is that much better, would it not |
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be the sane thing to recommend to users who read make.conf to use -O2? |
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I don't know - do -finline-functions and -frename-registers really make that |
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much of a difference? I am no expert at compiler internals. I only know what |
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has been my experience and what others say. |
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Just a thought. |
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|
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Matt |
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-- |
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gentoo-dev@g.o mailing list |
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