On Thursday, 07 July 2016 at 14:51, Ronald S. Bultje wrote: [...] > - start with one function. Take a really simple one. Don't do 20 at a time. > Especially if this is your first time writing ppc64 assembly. > - measure speedups on other archs with similar register width. Best > example: measure SSE2 vs. C. > - make sure you're measuring scalar C when measuring the base speed, since > x86 C vs. SSE2 is also scalar C vs. vector SIMD. There might be other > functions being picked up that we don't know about (some altivec is > BE-aware; your compiler might be auto-vectorizing C code. > - optimize your one function. Start with ideas taken from the x86 SSE2 > code. Use all things learned from x86 basics (do aligned loads where > possible, limit shuffles/data rearrangements, load constants outside loop, > etc.). > - measure. Use START/STOP_TIMER, nothing else, around the caller > with/without -cpuflags 0 and look only at the last reported cycle count > line. > - make changes. Measure again. Repeat. Do this with all suggestions from > code review also. Your test should be ultra-fast, something that takes 10 > seconds but invokes the function millions of times. If unsure, write a test > in checkasm, but usually one invocation from a fate test is good enough. > - if this is your first time writing assembly, you'll get tons of review > comments. This is normal, and we've all been through it. You'll become a > better coder for it, so learn from it, deal with it and keep submitting > patches until it's done. A few years from now, you'll be the expert > reviewer and an ever newer contributor will not yet know that he's about to > get learn some extremely important lessons from an experienced expert - you. > - once your first few individual functions are in, it may make sense to > submit sets of functions that are somehow related. However, this increases > review load so only do this once we know that you know what you're doing.
I think the above is very well written and could actually be used as a guide for new contributors. Thanks, Ronald. Regards, Dominik -- MPlayer http://mplayerhq.hu | RPM Fusion http://rpmfusion.org There should be a science of discontent. People need hard times and oppression to develop psychic muscles. -- from "Collected Sayings of Muad'Dib" by the Princess Irulan _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
