mirror of https://github.com/FFmpeg/FFmpeg.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
233 lines
7.5 KiB
233 lines
7.5 KiB
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. |
|
|
|
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 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 |
|
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 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 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 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: |
|
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 |
|
|
|
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
|
|
|