optimization Tips (for libavcodec):
What to optimize:
-if you plan to do non-x86 architecture specific optimiztions (SIMD normally) then
-take a look in the i386/ directory, as most important functions are allready
-optimized for MMX
+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.
-if u want to do x86 optimizations then u can either try to finetune the stuff in the
-i386 directory or find some other functions in the c source to optimize, but there
-arent many left
+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, like the c ones tend to be a bit unreadable currently becouse
-of optimizations it is difficult to understand them (and write arichtecture
-specific versions, or optimize the c functions further) it is recommanded to look
-at older CVS versions of the interresting files (just use CVSWEB at
-(http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ffmpeg/ffmpeg/libavcodec/))
-or perhaps look into the other architecture specific versions in i386/, ppc/,
-alpha/, ...; even if u dont understand the instructions exactly it could help
-understanding the functions & how they can be optimized
+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
+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
+the i386/, 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 u still dont understand some function then ask at our mailing list!!!
-(http://lists.sourceforge.net/lists/listinfo/ffmpeg-devel)
+NOTE: If you still don't understand some function, ask at our mailing list!!!
+(http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-devel)
-wtf is that function good for ....:
-the primary purpose of that list is to avoid wasting time to optimize functions
+WTF is that function good for ....:
+The primary purpose of that list is to avoid wasting time to optimize functions
which are rarely used
put(_no_rnd)_pixels{,_x2,_y2,_xy2}
- used in motion compensation (en/decoding)
+ Used in motion compensation (en/decoding).
avg_pixels{,_x2,_y2,_xy2}
- used in motion compensation of B Frames
- these are less important then the put*pixels functions
+ Used in motion compensation of B-frames.
+ These are less important than the put*pixels functions.
avg_no_rnd_pixels*
- unused
+ unused
pix_abs16x16{,_x2,_y2,_xy2}
- used in motion estimation (encoding) with SAD
+ Used in motion estimation (encoding) with SAD.
pix_abs8x8{,_x2,_y2,_xy2}
- used in motion estimation (encoding) with SAD of MPEG4 4MV only
- these are less important then the pix_abs16x16* functions
+ 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 recommanded that u waste ur time with these, as WMV2 is a
- ugly and relativly useless codec
+ 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*
- use in MPEG4 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
-
+ 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 workaround a bug in old libavcodec encoder
- dont optimze them
+ 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 optimze them if u need fast SVQ3 decoding
+ Used only for SVQ3, so only optimize them if you need fast SVQ3 decoding.
add_bytes/diff_bytes
- for huffyuv only, optimize if u want a faster ff-huffyuv codec
+ For huffyuv only, optimize if you want a faster ffhuffyuv codec.
get_pixels / diff_pixels
- used for encoding, easy
-
+ Used for encoding, easy.
+
clear_blocks
- easiest, to optimize
-
+ easiest to optimize
+
gmc
- used for mpeg4 gmc
- optimizing this should have a significant effect on the gmc decoding speed but
- its very likely impossible to write in SIMD
+ 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.
gmc1
- used for chroma blocks in mpeg4 gmc with 1 warp point
- (there are 4 luma & 2 chroma blocks per macrobock, 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
+ 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
-
+ 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
- dont waste ur time with dct_sad & quant_psnr they arent really usefull
+ 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
+ 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
-
+ idct (encoding & decoding)
+ fdct (encoding)
+ difficult to optimize
+
dct_quantize_trellis
- used for encoding with trellis quantization
- difficult to optimize
+ Used for encoding with trellis quantization.
+ difficult to optimize
dct_quantize
- used for encoding
-
+ Used for encoding.
+
dct_unquantize_mpeg1
- used in mpeg1 en/decoding
+ Used in MPEG-1 en/decoding.
dct_unquantize_mpeg2
- used in mpeg2 en/decoding
+ Used in MPEG-2 en/decoding.
dct_unquantize_h263
- used in mpeg4/h263 en/decoding
+ Used in MPEG-4/H.263 en/decoding.
FIXME remaining functions?
-btw, most of these are in dsputil.c/.h some are in mpegvideo.c/.h
+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 inctructios on X86
-the minimum guranteed alignment is writen in the .h files
-for example:
+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 DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size);
Links:
http://www.aggregate.org/MAGIC/
-X86 specific:
+x86-specific:
http://developer.intel.com/design/pentium4/manuals/248966.htm
-The IA-32 Intel Architecture Software Developer's Manual, Volume 2:
+The IA-32 Intel Architecture Software Developer's Manual, Volume 2:
Instruction Set Reference
http://developer.intel.com/design/pentium4/manuals/245471.htm
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:
+http://www.arm.com/community/academy/resources.html
+
+Instructions timings and optimization guide for ARM9E:
+http://www.arm.com/pdfs/DDI0222B_9EJS_r1p2.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 says its not)
+a bit old (note "+" is valid for input-output, even though the next disagrees)
http://www.cs.virginia.edu/~clc5q/gcc-inline-asm.pdf
-
projects / ffmpeg / blobdiff