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157 lines
5.0 KiB
157 lines
5.0 KiB
optimization Tips (for libavcodec): |
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What to optimize: |
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if u plan to do non-x86 architecture specific optimiztions (SIMD normally) then |
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take a look in the i386/ directory, as most important functions are allready |
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optimized for MMX |
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if u want to do x86 optimizations then u can either try to finetune the stuff in the |
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i386 directory or find some other functions in the c source to optimize, but there |
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arent many left |
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Understanding these overoptimized functions: |
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as many functions, like the c ones tend to be a bit unreadable currently becouse |
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of optimizations it is difficult to understand them (and write arichtecture |
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specific versions, or optimize the c functions further) it is recommanded to look |
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at older CVS versions of the interresting files (just use CVSWEB at |
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(http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ffmpeg/ffmpeg/libavcodec/)) |
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or perhaps look into the other architecture specific versions in i386/, ppc/, |
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alpha/, ...; even if u dont understand the instructions exactly it could help |
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understanding the functions & how they can be optimized |
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NOTE:!!! if u still dont understand some function then ask at our mailing list!!! |
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(http://lists.sourceforge.net/lists/listinfo/ffmpeg-devel) |
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wtf is that function good for ....: |
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the primary purpose of that list is to avoid wasting time to optimize functions |
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which are rarely used |
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put(_no_rnd)_pixels{,_x2,_y2,_xy2} |
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used in motion compensation (en/decoding) |
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avg_pixels{,_x2,_y2,_xy2} |
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used in motion compensation of B Frames |
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these are less important then the put*pixels functions |
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avg_no_rnd_pixels* |
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unused |
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pix_abs16x16{,_x2,_y2,_xy2} |
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used in motion estimation (encoding) with SAD |
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pix_abs8x8{,_x2,_y2,_xy2} |
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used in motion estimation (encoding) with SAD of MPEG4 4MV only |
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these are less important then the pix_abs16x16* functions |
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put_mspel8_mc* / wmv2_mspel8* |
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used only in WMV2 |
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it is not recommanded that u waste ur time with these, as WMV2 is a |
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ugly and relativly useless codec |
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mpeg4_qpel* / *qpel_mc* |
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use in MPEG4 qpel Motion compensation (encoding & decoding) |
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the qpel8 functions are used only for 4mv |
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the avg_* functions are used only for b frames |
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optimizing them should have a significant impact on qpel encoding & decoding |
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qpel{8,16}_mc??_old_c / *pixels{8,16}_l4 |
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just used to workaround a bug in old libavcodec encoder |
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dont optimze them |
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tpel_mc_func {put,avg}_tpel_pixels_tab |
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used only for SVQ3, so only optimze them if u need fast SVQ3 decoding |
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add_bytes/diff_bytes |
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for huffyuv only, optimize if u want a faster ff-huffyuv codec |
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get_pixels / diff_pixels |
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used for encoding, easy |
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clear_blocks |
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easiest, to optimize |
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gmc |
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used for mpeg4 gmc |
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optimizing this should have a significant effect on the gmc decoding speed but |
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its very likely impossible to write in SIMD |
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gmc1 |
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used for chroma blocks in mpeg4 gmc with 1 warp point |
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(there are 4 luma & 2 chroma blocks per macrobock, so |
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only 1/3 of the gmc blocks use this, the other 2/3 |
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use the normal put_pixel* code, but only if there is |
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just 1 warp point) |
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Note: Divx5 gmc always uses just 1 warp point |
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pix_sum |
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used for encoding |
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hadamard8_diff / sse / sad == pix_norm1 / dct_sad / quant_psnr / rd / bit |
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specific compare functions used in encoding, it depends upon the command line |
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switches which of these are used |
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dont waste ur time with dct_sad & quant_psnr they arent really usefull |
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put_pixels_clamped / add_pixels_clamped |
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used for en/decoding in the IDCT, easy |
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Note, some optimized IDCTs have the add/put clamped code included and then |
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put_pixels_clamped / add_pixels_clamped will be unused |
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idct/fdct |
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idct (encoding & decoding) |
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fdct (encoding) |
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difficult to optimize |
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dct_quantize_trellis |
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used for encoding with trellis quantization |
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difficult to optimize |
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dct_quantize |
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used for encoding |
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dct_unquantize_mpeg1 |
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used in mpeg1 en/decoding |
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dct_unquantize_mpeg2 |
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used in mpeg2 en/decoding |
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dct_unquantize_h263 |
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used in mpeg4/h263 en/decoding |
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FIXME remaining functions? |
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btw, most of these are in dsputil.c/.h some are in mpegvideo.c/.h |
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Alignment: |
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some instructions on some architectures have strict alignment restrictions, |
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for example most SSE/SSE2 inctructios on X86 |
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the minimum guranteed alignment is writen in the .h files |
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for example: |
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void (*put_pixels_clamped)(const DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size); |
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Links: |
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http://www.aggregate.org/MAGIC/ |
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X86 specific: |
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http://developer.intel.com/design/pentium4/manuals/248966.htm |
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The IA-32 Intel Architecture Software Developer's Manual, Volume 2: |
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Instruction Set Reference |
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http://developer.intel.com/design/pentium4/manuals/245471.htm |
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http://www.agner.org/assem/ |
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AMD Athlon Processor x86 Code Optimization Guide: |
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http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pdf |
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GCC asm links: |
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official doc but quite ugly |
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http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html |
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a bit old (note "+" is valid for input-output, even though the next says its not) |
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http://www.cs.virginia.edu/~clc5q/gcc-inline-asm.pdf |
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