[FFmpeg-devel] [PATCH] Remove global mm_flags variable

[Måns Rullgård]

Ivan Kalvachev <ikalvachev at gmail.com> writes:

> On 8/24/10, Michael Niedermayer <michaelni at gmx.at> wrote:
>> On Tue, Aug 24, 2010 at 10:39:30PM +0300, Ivan Kalvachev wrote:
>>> On 8/24/10, Mans Rullgard <mans at mansr.com> wrote:
>>> > -
>>> > -#define emms_c() \
>>> > -{\
>>> > -    if (mm_flags & FF_MM_MMX)\
>>> > -        emms();\
>>> > -}
>>> > +#define emms_c() emms()
>>>
>>> Michael, are you really OK with that change?
>>> The result would be illegal instruction on all pre-MMX CPUs.
>>
>> who still uses these?
>> and how much pre mmx x86 asm do we have? and how much faster is
>> that on pre mmx cpus?
>
> I think this is actually taking the issue backwards.
> You can build ffmpeg with optimizations for specific cpu. When
> building generic one, you would expect to be able to run on any kind
> of cpu.
>
> We do have ./configure -cpu= "select the minimum required CPU (affects
> selection, may crash on older CPUs)".
> I think we should use it.

Nothing changed.  A build that will run on a 486 will also run on a
Core i7.  The converse is not true and it never was.

> It's not only matter of convinience, it is also matter of principle.
> When you obsolate one class of CPU, doing the same with the next one
> would be logical step, going down the slippery slope.

Yes, the slope of time is dotted with new CPUs.

> And please don't ask _me_ for patches, I'm not the one breaking it.

No, you're the one complaining without cause.  As always.

-- 
M?ns Rullg?rd
mans at mansr.com