[x264-devel] Re: x264 improvement

[David Wolstencroft]

No Xcode needed :)

Make sure you build x264 with ./configure --enable-debug as this will make
using shark quite a bit easier. Once you launch shark, you can either launch
x264 from within shark or attach to the running process one you have already
spawned it. I tend to do the latter since I can tweak settings as I wish in
the terminal without having to set up the target again. Hot spots change
widely with the settings used.

Don't always count on shark being helpful - data mining, especially of
alignment has proven to give the most profound results for code improvement
so far. While Alignment isn't always perfect, you'll be surprised how
consistently out of alignment it is, and I do mean by out of Alignment by an
x amount of bytes :P. There's even a nice way to handle contiguous accesses
that start at an unaligned address. Remember that the PowerPC architecture
is roughly limited by the speed of which it can do loads and stores -
requesting more loads and stores that are needed hurts performance
considerably.


Also be weary of GCC's ability or inability to correctly unroll/schedule
loops.


If you really, really want to build x264 from within XCode, your best bet is
to set up a target using an external make file. Make sure you set the x264
Makefile as the target. It may make organization of the source easier, it
may not.

Anyway, I'll see as to what I can do with the code I have.



On 3/13/06, Eric Petit <titer at m0k.org> wrote:
>
>   You don't need Xcode for Shark - you can use Shark on any running
> application.
>
> Firas Al-Tahan wrote:
> > I'm certainly willing to try!
> >
> > Tim - have you been able to get the x264 code into XCode 2.1? I
> > haven't had much experience with XCode, and the book I bought  ("The
> > Mac XCode 2 Book" by Michael Cohen & Dennis Cohen) is a pile of crap.
> >
> > Having read the Apple pages, the Shark tool should help identify areas
> > needing optimization. Once I get XCode working with the x264 project,
> > il be happy.
> >
> > Now, just to finish off the coursework and the exams first....
> >
> > Firas
> >
> > On 3/13/06, Tim Greatrex < tim.greatrex at mac.com> wrote:
> >> I'm guessing the issue may be that he has worked on this in his spare
> >> time, while he works for a company that develops a different codec
> >> which it then sells (so x264 is classed as the competition). I
> >> doesn't sound like there are any legal issues with the code he's
> >> developed, but maybe moral issues for his position within his day-job.
> >>
> >> As a mac user (who is very new to c and at the moment can't make head-
> >> nor-tail of the x264 code (though it works great!), let alone altivec
> >> optimisations) it would be great if you could make it available,
> >> especially with some good annotations describing what does what if
> >> possible, so that myself and people like Firas can learn from you.
> >>
>
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