On Di, Jan 24, 2012 at 16:09:01 (CET), Felipe Sateler wrote: > On Tue, Jan 24, 2012 at 09:11, Reinhard Tartler <siret...@tauware.de> wrote: >> On Di, Jan 24, 2012 at 11:04:00 (CET), Fabian Greffrath wrote: >> >>> Am 23.01.2012 14:53, schrieb Reinhard Tartler: >>>> The reason is that x264 uses a lot of hand written assembler, and >>>> upstream takes care to use non-pic code only on architectures that >>>> support this. >>>> >>>> Btw, the same applies to the libav* packages. >>> >>> Is there any benchmark available (for either package) that compares the >>> performance of the library using the hand written assambler code with >>> one using generic code? >> >> Have a look at upstream commit logs. Many commit messages count cpu >> cycles as performance speedup. >> >> http://git.videolan.org/?p=x264.git;a=commitdiff;h=748fe16c1303b89d2a1d0378addd83fb4198f51a >> http://git.videolan.org/?p=x264.git;a=commitdiff;h=6b06f6d3f7f800dca1a4ea154f54427d5b3cea2b >> >> no name only some very recent ones. > > Not that I'm an expert on this subject (and I haven't looked at the > code), but it is my understanding that cpu cycles is not the only > relevant measure of speed. Branching and the guessing the cpu does to > follow branches can be very relevant too. Code compactness is also > important due to cache hits/misses. So I think the only way to tell if > an optimization really is beneficial is via benchmarking.
You're right. My point is that x264 upstream is very well at micro optimizing the assembly and does a lot of both micro-benchmarks as well as encoding benchmarks on a regular basis. Please also note that just removing -fPIC from the makefiles will lead to compilation failures on i386 because of register shortage. You would then to additionally need to pass --disable-optimizations to the configure script. And now things will become really dogslow. Cheers, Reinhard -- Gruesse/greetings, Reinhard Tartler, KeyID 945348A4 _______________________________________________ pkg-multimedia-maintainers mailing list pkg-multimedia-maintainers@lists.alioth.debian.org http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/pkg-multimedia-maintainers
