| 1 |
On Mon, Oct 05, 2015 at 12:38:15AM +0200, Alan McKinnon wrote: |
| 2 |
> On 04/10/2015 22:49, James Cloos wrote: |
| 3 |
> > |
| 4 |
> > And is there really any value from micromanaging things like that in an |
| 5 |
> > ebuild? |
| 6 |
> |
| 7 |
> For ffmpeg? Yes. |
| 8 |
|
| 9 |
Actually, I think modern versions of ffmpeg probably do not benefit as |
| 10 |
much anymore. The `cpudetection' USE flag makes me think ffmpeg uses |
| 11 |
the CPUID instruction to determine which x86 extensions are available, |
| 12 |
and loads the appropriate code. This would enable Ubuntu et. al. to |
| 13 |
build ffmpeg with all the high performance code compiled, and still be |
| 14 |
compatible with all CPUs. I do not know if that is 100% true, but having |
| 15 |
a `cpudetection' USE flag makes me assume that's how it works. More on |
| 16 |
this here, which is the top of list when I searched "ffmpeg cpu |
| 17 |
detection" [1]. |
| 18 |
|
| 19 |
> I imagine users who rely on will be mighty upset if the |
| 20 |
> ebuild did not offer those flags. By way of example, many folks here |
| 21 |
> have reported their own experience over the years that a given cpu with |
| 22 |
> a standard Ubuntu i586 or so install struggles to keep up with a video. |
| 23 |
> The same hardware running the same software on Gentoo with sane options |
| 24 |
> and USE easily manages. That's the difference between managing and not |
| 25 |
> managing such things in areas where it matters. |
| 26 |
|
| 27 |
For plenty of packages, such as fftw, this is a huge benefit. fftw does |
| 28 |
not have a `cpudetection' USE flag, so I would assume that sse, avx, |
| 29 |
etc. must be determined at build time and can't be changed at runtime. |
| 30 |
|
| 31 |
Alec |
| 32 |
|
| 33 |
1. http://ffmpeg.org/pipermail/ffmpeg-devel/2012-September/131550.html |
Archives