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Diffstat (limited to 'contrib/ffmpeg/doc/optimization.txt')
| -rw-r--r-- | contrib/ffmpeg/doc/optimization.txt | 82 |
1 files changed, 74 insertions, 8 deletions
diff --git a/contrib/ffmpeg/doc/optimization.txt b/contrib/ffmpeg/doc/optimization.txt index f66c69bcf..4c0934b4b 100644 --- a/contrib/ffmpeg/doc/optimization.txt +++ b/contrib/ffmpeg/doc/optimization.txt @@ -1,6 +1,8 @@ optimization Tips (for libavcodec): +=================================== What to optimize: +----------------- If you plan to do non-x86 architecture specific optimizations (SIMD normally), then take a look in the i386/ directory, as most important functions are already optimized for MMX. @@ -9,10 +11,12 @@ If you want to do x86 optimizations then you can either try to finetune the stuff in the i386 directory or find some other functions in the C source to optimize, but there aren't many left. + Understanding these overoptimized functions: +-------------------------------------------- As many functions tend to be a bit difficult to understand because of optimizations, it can be hard to optimize them further, or write -architecture-specific versions. It is recommened to look at older +architecture-specific versions. It is recommended to look at older revisions of the interesting files (for a web frontend try ViewVC at http://svn.mplayerhq.hu/ffmpeg/trunk/). Alternatively, look into the other architecture-specific versions in @@ -24,10 +28,23 @@ NOTE: If you still don't understand some function, ask at our mailing list!!! (http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-devel) +When is an optimization justified? +---------------------------------- +Normally, clean and simple optimizations for widely used codecs are +justified even if they only achieve an overall speedup of 0.1%. These +speedups accumulate and can make a big difference after awhile. Also, if +none of the following factors get worse due to an optimization -- speed, +binary code size, source size, source readability -- and at least one +factor improves, then an optimization is always a good idea even if the +overall gain is less than 0.1%. For obscure codecs that are not often +used, the goal is more toward keeping the code clean, small, and +readable instead of making it 1% faster. + WTF is that function good for ....: -The primary purpose of that list is to avoid wasting time to optimize functions -which are rarely used +----------------------------------- +The primary purpose of this list is to avoid wasting time optimizing functions +which are rarely used. put(_no_rnd)_pixels{,_x2,_y2,_xy2} Used in motion compensation (en/decoding). @@ -77,7 +94,7 @@ clear_blocks gmc Used for MPEG-4 gmc. Optimizing this should have a significant effect on the gmc decoding - speed but it's very likely impossible to write in SIMD. + speed. gmc1 Used for chroma blocks in MPEG-4 gmc with 1 warp point @@ -134,11 +151,29 @@ The minimum guaranteed alignment is written in the .h files, for example: void (*put_pixels_clamped)(const DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size); +General Tips: +------------- +Use asm loops like: +asm( + "1: .... + ... + "jump_instruciton .... +Do not use C loops: +do{ + asm( + ... +}while() + +Use asm() instead of intrinsics. The latter requires a good optimizing compiler +which gcc is not. + Links: +====== http://www.aggregate.org/MAGIC/ x86-specific: +------------- http://developer.intel.com/design/pentium4/manuals/248966.htm The IA-32 Intel Architecture Software Developer's Manual, Volume 2: @@ -152,14 +187,45 @@ http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pd ARM-specific: -ARM Architecture Reference Manual: -http://www.arm.com/community/academy/resources.html +------------- +ARM Architecture Reference Manual (up to ARMv5TE): +http://www.arm.com/community/university/eulaarmarm.html + +Procedure Call Standard for the ARM Architecture: +http://www.arm.com/pdfs/aapcs.pdf + +Optimization guide for ARM9E (used in Nokia 770 Internet Tablet): +http://infocenter.arm.com/help/topic/com.arm.doc.ddi0240b/DDI0240A.pdf +Optimization guide for ARM11 (used in Nokia N800 Internet Tablet): +http://infocenter.arm.com/help/topic/com.arm.doc.ddi0211j/DDI0211J_arm1136_r1p5_trm.pdf +Optimization guide for Intel XScale (used in Sharp Zaurus PDA): +http://download.intel.com/design/intelxscale/27347302.pdf + +PowerPC-specific: +----------------- +PowerPC32/AltiVec PIM: +www.freescale.com/files/32bit/doc/ref_manual/ALTIVECPEM.pdf + +PowerPC32/AltiVec PEM: +www.freescale.com/files/32bit/doc/ref_manual/ALTIVECPIM.pdf + +CELL/SPU: +http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/30B3520C93F437AB87257060006FFE5E/$file/Language_Extensions_for_CBEA_2.4.pdf +http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/9F820A5FFA3ECE8C8725716A0062585F/$file/CBE_Handbook_v1.1_24APR2007_pub.pdf + +SPARC-specific: +--------------- +SPARC Joint Programming Specification (JPS1): Commonality +http://www.fujitsu.com/downloads/PRMPWR/JPS1-R1.0.4-Common-pub.pdf -Instructions timings and optimization guide for ARM9E: -http://www.arm.com/pdfs/DDI0222B_9EJS_r1p2.pdf +UltraSPARC III Processor User's Manual (contains instruction timings) +http://www.sun.com/processors/manuals/USIIIv2.pdf +VIS Whitepaper (contains optimization guidelines) +http://www.sun.com/processors/vis/download/vis/vis_whitepaper.pdf GCC asm links: +-------------- official doc but quite ugly http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html |