[FFmpeg-devel] [PATCH] Add check for Athlon64 and similar AMD processors with slow SSE2.

Ronald S. Bultje rsbultje
Fri Feb 4 18:27:41 CET 2011


On Thu, Feb 3, 2011 at 7:04 PM, Justin Ruggles <justin.ruggles at gmail.com> wrote:
> On 02/03/2011 01:58 AM, Jason Garrett-Glaser wrote:
>> On Wed, Feb 2, 2011 at 3:26 PM, Justin Ruggles <justin.ruggles at gmail.com> wrote:
>>> ---
>>> This was ported from x264 so we need permission to relicense from
>>> Loren, Jason, or whoever added this particular check in x264.
>> That's one line of code, it's too trivial to matter.
>> But keep in mind that SSE2SLOW seems to mean something different in
>> ffmpeg. ?It's already used for the case of Core 1, where SSE2 is
>> ALMOST ALWAYS slower than MMX. ?But on Athlon 64, it's mostly faster,
>> just slower in some cases.
> Yes, but it's still possible to reuse this flag because we disable
> AV_CPU_FLAG_SSE2 in the case of Core 1. ?Although it would make things
> slightly more complex in the case where you want to enable an SSE2
> function on Core 1 but disable it on Athlon64. ?So I'll send a new patch
> that adds a separate flag.

I'm not against the original idea of reusing SSE2SLOW, just make sure
it's properly documented.
- SSE2 - CPU supports good SSE2
- SSE2SLOW (core1 etc.) - CPU supports SSE2 in theory but it's almost
always slower - only set SSE2 functions if explicitely tested to be
- SSE2|SSE2SLOW (athlon64 etc.) - CPU supports SSE2 but it's
occasionaly slower - don't set SSE2 functions if explicitely tested to
be slower

And I thought that's what your patch did.


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