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diff --git a/ffmpeg/doc/optimization.txt b/ffmpeg/doc/optimization.txt deleted file mode 100644 index 5a66d6b..0000000 --- a/ffmpeg/doc/optimization.txt +++ /dev/null @@ -1,288 +0,0 @@ -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 x86/ directory, as most important functions are -already optimized for MMX. - -If you want to do x86 optimizations then you can either try to finetune the -stuff in the x86 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 recommended to look at older -revisions of the interesting files (web frontends for the various FFmpeg -branches are listed at http://ffmpeg.org/download.html). -Alternatively, look into the other architecture-specific versions in -the x86/, ppc/, alpha/ subdirectories. Even if you don't exactly -comprehend the instructions, it could help understanding the functions -and how they can be optimized. - -NOTE: If you still don't understand some function, ask at our mailing list!!! -(http://lists.ffmpeg.org/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 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). - -avg_pixels{,_x2,_y2,_xy2} - Used in motion compensation of B-frames. - These are less important than the put*pixels functions. - -avg_no_rnd_pixels* - unused - -pix_abs16x16{,_x2,_y2,_xy2} - Used in motion estimation (encoding) with SAD. - -pix_abs8x8{,_x2,_y2,_xy2} - Used in motion estimation (encoding) with SAD of MPEG-4 4MV only. - These are less important than the pix_abs16x16* functions. - -put_mspel8_mc* / wmv2_mspel8* - Used only in WMV2. - it is not recommended that you waste your time with these, as WMV2 - is an ugly and relatively useless codec. - -mpeg4_qpel* / *qpel_mc* - Used in MPEG-4 qpel motion compensation (encoding & decoding). - The qpel8 functions are used only for 4mv, - the avg_* functions are used only for B-frames. - Optimizing them should have a significant impact on qpel - encoding & decoding. - -qpel{8,16}_mc??_old_c / *pixels{8,16}_l4 - Just used to work around a bug in an old libavcodec encoder version. - Don't optimize them. - -tpel_mc_func {put,avg}_tpel_pixels_tab - Used only for SVQ3, so only optimize them if you need fast SVQ3 decoding. - -add_bytes/diff_bytes - For huffyuv only, optimize if you want a faster ffhuffyuv codec. - -get_pixels / diff_pixels - Used for encoding, easy. - -clear_blocks - easiest to optimize - -gmc - Used for MPEG-4 gmc. - Optimizing this should have a significant effect on the gmc decoding - speed. - -gmc1 - Used for chroma blocks in MPEG-4 gmc with 1 warp point - (there are 4 luma & 2 chroma blocks per macroblock, so - only 1/3 of the gmc blocks use this, the other 2/3 - use the normal put_pixel* code, but only if there is - just 1 warp point). - Note: DivX5 gmc always uses just 1 warp point. - -pix_sum - Used for encoding. - -hadamard8_diff / sse / sad == pix_norm1 / dct_sad / quant_psnr / rd / bit - Specific compare functions used in encoding, it depends upon the - command line switches which of these are used. - Don't waste your time with dct_sad & quant_psnr, they aren't - really useful. - -put_pixels_clamped / add_pixels_clamped - Used for en/decoding in the IDCT, easy. - Note, some optimized IDCTs have the add/put clamped code included and - then put_pixels_clamped / add_pixels_clamped will be unused. - -idct/fdct - idct (encoding & decoding) - fdct (encoding) - difficult to optimize - -dct_quantize_trellis - Used for encoding with trellis quantization. - difficult to optimize - -dct_quantize - Used for encoding. - -dct_unquantize_mpeg1 - Used in MPEG-1 en/decoding. - -dct_unquantize_mpeg2 - Used in MPEG-2 en/decoding. - -dct_unquantize_h263 - Used in MPEG-4/H.263 en/decoding. - -FIXME remaining functions? -BTW, most of these functions are in dsputil.c/.h, some are in mpegvideo.c/.h. - - - -Alignment: -Some instructions on some architectures have strict alignment restrictions, -for example most SSE/SSE2 instructions on x86. -The minimum guaranteed alignment is written in the .h files, for example: - void (*put_pixels_clamped)(const int16_t *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size); - - -General Tips: -------------- -Use asm loops like: -__asm__( - "1: .... - ... - "jump_instruction .... -Do not use C loops: -do{ - __asm__( - ... -}while() - -For x86, mark registers that are clobbered in your asm. This means both -general x86 registers (e.g. eax) as well as XMM registers. This last one is -particularly important on Win64, where xmm6-15 are callee-save, and not -restoring their contents leads to undefined results. In external asm (e.g. -yasm), you do this by using: -cglobal functon_name, num_args, num_regs, num_xmm_regs -In inline asm, you specify clobbered registers at the end of your asm: -__asm__(".." ::: "%eax"). -If gcc is not set to support sse (-msse) it will not accept xmm registers -in the clobber list. For that we use two macros to declare the clobbers. -XMM_CLOBBERS should be used when there are other clobbers, for example: -__asm__(".." ::: XMM_CLOBBERS("xmm0",) "eax"); -and XMM_CLOBBERS_ONLY should be used when the only clobbers are xmm registers: -__asm__(".." :: XMM_CLOBBERS_ONLY("xmm0")); - -Do not expect a compiler to maintain values in your registers between separate -(inline) asm code blocks. It is not required to. For example, this is bad: -__asm__("movdqa %0, %%xmm7" : src); -/* do something */ -__asm__("movdqa %%xmm7, %1" : dst); -- first of all, you're assuming that the compiler will not use xmm7 in - between the two asm blocks. It probably won't when you test it, but it's - a poor assumption that will break at some point for some --cpu compiler flag -- secondly, you didn't mark xmm7 as clobbered. If you did, the compiler would - have restored the original value of xmm7 after the first asm block, thus - rendering the combination of the two blocks of code invalid -Code that depends on data in registries being untouched, should be written as -a single __asm__() statement. Ideally, a single function contains only one -__asm__() block. - -Use external asm (nasm/yasm) or inline asm (__asm__()), do not use intrinsics. -The latter requires a good optimizing compiler which gcc is not. - -Inline asm vs. external asm ---------------------------- -Both inline asm (__asm__("..") in a .c file, handled by a compiler such as gcc) -and external asm (.s or .asm files, handled by an assembler such as yasm/nasm) -are accepted in FFmpeg. Which one to use differs per specific case. - -- if your code is intended to be inlined in a C function, inline asm is always - better, because external asm cannot be inlined -- if your code calls external functions, yasm is always better -- if your code takes huge and complex structs as function arguments (e.g. - MpegEncContext; note that this is not ideal and is discouraged if there - are alternatives), then inline asm is always better, because predicting - member offsets in complex structs is almost impossible. It's safest to let - the compiler take care of that -- in many cases, both can be used and it just depends on the preference of the - person writing the asm. For new asm, the choice is up to you. For existing - asm, you'll likely want to maintain whatever form it is currently in unless - there is a good reason to change it. -- if, for some reason, you believe that a particular chunk of existing external - asm could be improved upon further if written in inline asm (or the other - way around), then please make the move from external asm <-> inline asm a - separate patch before your patches that actually improve the asm. - - -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: -Instruction Set Reference -http://developer.intel.com/design/pentium4/manuals/245471.htm - -http://www.agner.org/assem/ - -AMD Athlon Processor x86 Code Optimization Guide: -http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pdf - - -ARM-specific: -------------- -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 -Intel Wireless MMX 2 Coprocessor: Programmers Reference Manual -http://download.intel.com/design/intelxscale/31451001.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 - -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 - -a bit old (note "+" is valid for input-output, even though the next disagrees) -http://www.cs.virginia.edu/~clc5q/gcc-inline-asm.pdf |