[FFmpeg-devel] [PATCH] Fix configure to disable MMX for Pentium Pro

Jason Garrett-Glaser darkshikari
Thu Aug 26 16:48:25 CEST 2010


2010/8/26 M?ns Rullg?rd <mans at mansr.com>:
> "Ronald S. Bultje" <rsbultje at gmail.com> writes:
>
>> Hi,
>>
>> On Thu, Aug 26, 2010 at 9:34 AM, Alex Converse <alex.converse at gmail.com> wrote:
>>> ./configure --cpu=prentiumpro says build me an FFmpeg for a
>>> PentiumPro. The result will no longer run on a PentiumPro.
>>
>> A) It should require --disable-mmx (and thus the configure patch to
>> disable mmx should be changed to error out unless mmx is disabled),
>
> That's a stupid idea. ?Specifying a CPU without MMX should of course
> disable MMX. ?That stands to reason. ?It is also how all the other
> architectures work.
>
>> B) we should revert the mmx-requiring commit and only do unconditional
>> emms on x86-64 (I think this is acceptable. Mans?).
>
> The main point of the change was to get rid of the stupid global
> mm_flags variable. ?We discussed it at length some time ago (it nearly
> went full bikeshed), and nobody objected then, not even the distro people.
> Why the sudden outrage?

Whether we like it or not, a huge number of people compile ffmpeg with
--cpu=i686 or similar for generic builds.  With these changes,
--cpu=i686 will actually SLOW DOWN ffmpeg as opposed to not specifying
CPU at all.  This is not intuitive behavior.

Dark Shikari



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