Hi, On Thu, Jul 26, 2012 at 9:05 AM, Måns Rullgård <m...@mansr.com> wrote: > "Ronald S. Bultje" <rsbul...@gmail.com> writes: >> On Thu, Jul 26, 2012 at 7:30 AM, Martin Storsjö <mar...@martin.st> wrote: >>> On Thu, 26 Jul 2012, Ronald S. Bultje wrote: >>>> On Thu, Jul 26, 2012 at 2:06 AM, Diego Biurrun <di...@biurrun.de> wrote: >>>>> On Thu, Jul 26, 2012 at 05:10:10AM +0200, Luca Barbato wrote: >>>>>> On 07/26/2012 04:27 AM, Ronald S. Bultje wrote: >>>>>>> From: "Ronald S. Bultje" <rsbul...@gmail.com> >>>>>>> >>>>>>> --- >>>>>>> libswscale/swscale.c | 2 +- >>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>> >>>>>> >>>>>> Ok. >>>>> >>>>> >>>>> No, not OK. This is just a repackaged piece of another patch that >>>>> has review questions that were never answered. Until those questions >>>>> are settled, this cannot go in. >>>> >>>> >>>> I've looked at all emails in: >>>> http://comments.gmane.org/gmane.comp.video.libav.devel/28861 >>>> >>>> including yours: >>>> http://permalink.gmane.org/gmane.comp.video.libav.devel/28871 >>>> >>>> and Mans': >>>> http://permalink.gmane.org/gmane.comp.video.libav.devel/28863 >>>> >>>> My original mail has the "fence" part in it (simply ctrl-F in your >>>> browser), and neither you nor Mans respond to that particular section. >>>> So I'm lost now. What is the specific comment you want me to respond >>>> to? >>> >>> >>> http://article.gmane.org/gmane.comp.video.libav.devel/30834 >> >> If someone feels like rewriting swscale, I'm all supportive of that >> effort. For now, sws uses movntq in its inline assembly mmx/3dnow >> optimizations and we'll have to deal with it until someone changes it >> not to do that. >> >> Doing it in generic code is silly because in practice there is never >> any advantage to doing movntq. Thus, we should discourage its use. >> Adding generic versions of sfence does not contribute to that. The >> whole goal - back when I worked on sws - was to kill all these old >> mmx/3dnow optimizations and replace with modern sse2/avx, which would >> mean we don't need a call to sfence anymore anyways. > > I'm still missing an explanation of why sfence is needed here other than > movntq somehow being involved.
My understanding is that if you use movntq and not sfence, the data may not be in the destination memory pointer by the time swScale() returns. But I didn't write this code. Ronald _______________________________________________ libav-devel mailing list libav-devel@libav.org https://lists.libav.org/mailman/listinfo/libav-devel
