> On 12 Jan 2021, at 19:52, Soft Works <[email protected]> wrote: > > > >> -----Original Message----- >> From: ffmpeg-devel <[email protected]> On Behalf Of >> [email protected] >> Sent: Sunday, January 10, 2021 5:44 PM >> To: [email protected] >> Cc: Reimar Döffinger <[email protected]> >> Subject: [FFmpeg-devel] [PATCH] Add support for "omp simd" pragma. >> >> From: Reimar Döffinger <[email protected]> >> >> This requests loops to be vectorized using SIMD instructions. >> The performance increase is far from hand-optimized assembly but still >> significant over the plain C version. >> Typical values are a 2-4x speedup where a hand-written version would >> achieve 4x-10x. >> So it is far from a replacement, however some architures will get hand- >> written assembler quite late or not at all, and this is a good improvement >> for >> a trivial amount of work. >> The cause, besides the compiler being a compiler, is usually that it does not >> manage to use saturating instructions and thus has to use 32-bit operations >> where actually saturating 16-bit operations would be sufficient. >> Other causes are for example the av_clip functions that are not ideal for >> vectorization (and even as scalar code not optimal for any modern CPU that >> has either CSEL or MAX/MIN instructions). >> And of course this only works for relatively simple loops, the IDCT functions >> for example seemed not possible to optimize that way. > > ... > >> +if enabled openmp_simd; then >> + ompopt="-fopenmp" >> + if ! test_cflags $ompopt ; then >> + test_cflags -Xpreprocessor -fopenmp && ompopt="-Xpreprocessor - >> fopenmp" > > Isn't it sufficient to specify -fopenmp-simd instead of -fopenmp for this > patch?
I think so, I just didn’t know/even expect that option to exist! Thanks a lot for the tip! > As OMP SIMD is the only openmp feature that is used, there's no need to link > to the openmp lib. That it doesn’t do anyway because -fopenmp is not in the linker flags, but I admit that was a bit of a hacky solution. Thanks, Reimar _______________________________________________ ffmpeg-devel mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
