compilation architecture

[Jakub 'Livio' Rusinek]

2008/1/14, Callum Lerwick <seg at haxxed.com>:
>
>
> On Sat, 2008-01-12 at 18:51 +0100, drago01 wrote:
> > 2008/1/12 Jakub 'Livio' Rusinek <jakub.rusinek at gmail.com>:
> > > do we need to support legacy cpu's by i386 compilation?
> > > i586 would make fedora faster even 3 times.
> > > difference is noticeable.
> >
> > .....
> > where are your benchmarks for the "3 times faster" claim?
> > the i386 packages are already optimized for newer cpus (mtune vs. march)
> > where it makes sense to have i686 versions there are some (kernel,
> glibc)
>
> Lets get some real numbers in here. For a quick and dirty benchmark I'm
> using OpenJPEG's MJ2 tools, I encode the speedway example using
> "frames_to_mj2 -i Speedway.yuv -o Speedway.mj2 -I 1", then decode it.
> I'm measuring the decode time. Tests were performed on a Mobile Celeron
> 1.3, which is P3 architecture.
>
> Here it is with -march=i386 -mcpu=generic. That is, standard Fedora
> flags:
>
> Total decoding time: 21.14 seconds (9.5 fps)
>
> With -march=i586 -mcpu=generic:
>
> Total decoding time: 21.26 seconds (9.4 fps)
>
> And -march=i686 -mcpu=generic:
>
> Total decoding time: 20.45 seconds (9.8 fps)
>
> So it is 0.54% *slower* when compiled for i586, which is unexpected and
> strange, but such is gcc. I wouldn't expect much of a speed difference
> compiling for i586, there was no major additions to the instruction set,
> and we're already scheduling for modern processors.
>
> Not quite "three times" faster, but 3.26% faster with i686. A major
> addition to the i686 architecture was cmov, and gcc is actually very
> aggressive about eliminating branching using cmovs, increasing
> performance on modern deeply pipelined processors by eliminating
> pipeline stalls.
>
> And yes, cmov is technically optional, earlier VIA C3 processors, still
> being sold, lack it. Completely dropping support for pre-i686 just isn't
> an option yet.
>
> If Smolt is to be believed, i686 machines are 99.43% (!) of all x86
> machines. (Though I don't know if those pesky C3's are being counted as
> i686 or i586 or what...) I think its safe to say the vast majority of
> x86 systems out there have cmov, and are suffering with reduced
> performance in order to cater to a minority of systems.
>
> I suggest all key performance critical packages be made available in
> both i386 and i686 versions. glibc and openssl already do this. Off the
> top of my head, this would include Mesa, I know for a fact the majority
> of Second Life runtime is actually consumed by T&L inside Mesa/DRI. From
> what I understand, even Intel's latest chipsets lack hardware T&L. Makes
> sense, it helps sell more multi-core Intel processors, and probably
> helps consolidate power management.
>
> Also, all multimedia codecs. Old sub-Ghz machines have a lot of trouble
> playing the MPEG4 video that is common these days, and MythTV could use
> all the help it can get. Not that the MPEG4 codecs are in Fedora
> itself...
>
> Not that any of this has anything to do with the "firefox startup is
> slow" complaint that this thread has devolved into.
>
> --
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> https://www.redhat.com/mailman/listinfo/fedora-devel-list
>
>
I have no idea, why Firefox 3 starts in Fedora so long and scrolls in smooth
mode so long (with hanging for a while). Maybe it's Mesa compilation issue.
Xorg? I don't know.

I can only say that I want Fedora to be stable as rock, powerful and
beautiful.
No matter how we can do it.

I sad my words few times and did nothing, it's true, but it's because I
didn't know what I could really do.

About compilation: preloading is probably making everything in openSUSE load
faster, but how to implement this in Fedora? I'll invesigate where's their
SVN/CVS/GIT/MNT/etc.

-- 
Jakub 'Livio' Rusinek
http://liviopl.jogger.pl/
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