On 26/10/14 5:34 AM, Reimar Döffinger wrote: > On 26.10.2014, at 02:32, James Almer <jamr...@gmail.com> wrote: >> __sync built-ins are considered legacy and will be deprecated. >> These new memory model aware built-ins have been available since GCC 4.7.0 > > To me this sounds like "except for tsan, these new functions are worse in > every aspect, and that's with gcc 4.9, who knows what mess 4.7 will make of > them". > That sounds like a very bad argument to use them by default.
It's more like "Except for the compare and exchange function, these are either the same or better/more flexible". GCC even converts calls certain calls to __sync into the relevant __atomic at built time. > Nothing against also supporting them, but to make them default I don't think > any performance regressions are acceptable, and we need to either test 4.7 as > well or there must be a measurable performance advantage. The only one where it's almost a given a performance hit will be seen is with compare and excange, and that's why i asked if should keep using the __sync counterpart instead. The rest are the same, and will potentially perform better if we choose a more relaxed model. > IMHO. > Note that ARM might benefit a lot if you manage to use the less strict > versions. Ah, you just made realize i put x86 in the subject by mistake. > However since it might not make a difference on x86 testing that they work > properly might be difficult. > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
