Statistics
| Branch: | Revision:

ffmpeg / doc / optimization.txt @ dc7f38f5

History | View | Annotate | Download (7.67 KB)

1 a552591f Michael Niedermayer
optimization Tips (for libavcodec):
2 5e123bd3 Michael Niedermayer
===================================
3 a552591f Michael Niedermayer
4
What to optimize:
5 5e123bd3 Michael Niedermayer
-----------------
6 c5a44f57 Diego Biurrun
If you plan to do non-x86 architecture specific optimizations (SIMD normally),
7 a6493a8f Diego Biurrun
then take a look in the x86/ directory, as most important functions are
8 8ea9ce41 Diego Biurrun
already optimized for MMX.
9 a552591f Michael Niedermayer
10 8ea9ce41 Diego Biurrun
If you want to do x86 optimizations then you can either try to finetune the
11 a6493a8f Diego Biurrun
stuff in the x86 directory or find some other functions in the C source to
12 8ea9ce41 Diego Biurrun
optimize, but there aren't many left.
13 a552591f Michael Niedermayer
14 5e123bd3 Michael Niedermayer
15 a552591f Michael Niedermayer
Understanding these overoptimized functions:
16 5e123bd3 Michael Niedermayer
--------------------------------------------
17 0a46c933 Diego Biurrun
As many functions tend to be a bit difficult to understand because
18
of optimizations, it can be hard to optimize them further, or write
19 6609f9e2 Mike Melanson
architecture-specific versions. It is recommended to look at older
20 1c1b5a40 Diego Biurrun
revisions of the interesting files (for a web frontend try ViewVC at
21 0fa5f24c Diego Biurrun
http://svn.ffmpeg.org/ffmpeg/trunk/).
22 0a46c933 Diego Biurrun
Alternatively, look into the other architecture-specific versions in
23 a6493a8f Diego Biurrun
the x86/, ppc/, alpha/ subdirectories. Even if you don't exactly
24 0a46c933 Diego Biurrun
comprehend the instructions, it could help understanding the functions
25
and how they can be optimized.
26 8ea9ce41 Diego Biurrun
27
NOTE: If you still don't understand some function, ask at our mailing list!!!
28 2b165e29 Diego Biurrun
(http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-devel)
29 a552591f Michael Niedermayer
30 5e123bd3 Michael Niedermayer
31 ac59e7f4 Mike Melanson
When is an optimization justified?
32
----------------------------------
33 07bf0cc9 Mike Melanson
Normally, clean and simple optimizations for widely used codecs are
34
justified even if they only achieve an overall speedup of 0.1%. These
35
speedups accumulate and can make a big difference after awhile. Also, if
36
none of the following factors get worse due to an optimization -- speed,
37
binary code size, source size, source readability -- and at least one
38
factor improves, then an optimization is always a good idea even if the
39
overall gain is less than 0.1%. For obscure codecs that are not often
40
used, the goal is more toward keeping the code clean, small, and
41
readable instead of making it 1% faster.
42 a552591f Michael Niedermayer
43
44 8ea9ce41 Diego Biurrun
WTF is that function good for ....:
45 5e123bd3 Michael Niedermayer
-----------------------------------
46 6609f9e2 Mike Melanson
The primary purpose of this list is to avoid wasting time optimizing functions
47
which are rarely used.
48 a552591f Michael Niedermayer
49
put(_no_rnd)_pixels{,_x2,_y2,_xy2}
50 8ea9ce41 Diego Biurrun
    Used in motion compensation (en/decoding).
51 a552591f Michael Niedermayer
52
avg_pixels{,_x2,_y2,_xy2}
53 8ea9ce41 Diego Biurrun
    Used in motion compensation of B-frames.
54 c5a44f57 Diego Biurrun
    These are less important than the put*pixels functions.
55 a552591f Michael Niedermayer
56
avg_no_rnd_pixels*
57 38aca760 Diego Biurrun
    unused
58 a552591f Michael Niedermayer
59
pix_abs16x16{,_x2,_y2,_xy2}
60 8ea9ce41 Diego Biurrun
    Used in motion estimation (encoding) with SAD.
61 a552591f Michael Niedermayer
62
pix_abs8x8{,_x2,_y2,_xy2}
63 8ea9ce41 Diego Biurrun
    Used in motion estimation (encoding) with SAD of MPEG-4 4MV only.
64 c5a44f57 Diego Biurrun
    These are less important than the pix_abs16x16* functions.
65 a552591f Michael Niedermayer
66
put_mspel8_mc* / wmv2_mspel8*
67 8ea9ce41 Diego Biurrun
    Used only in WMV2.
68
    it is not recommended that you waste your time with these, as WMV2
69
    is an ugly and relatively useless codec.
70 a552591f Michael Niedermayer
71
mpeg4_qpel* / *qpel_mc*
72 8ea9ce41 Diego Biurrun
    Used in MPEG-4 qpel motion compensation (encoding & decoding).
73
    The qpel8 functions are used only for 4mv,
74
    the avg_* functions are used only for B-frames.
75
    Optimizing them should have a significant impact on qpel
76
    encoding & decoding.
77 38aca760 Diego Biurrun
78 a552591f Michael Niedermayer
qpel{8,16}_mc??_old_c / *pixels{8,16}_l4
79 8ea9ce41 Diego Biurrun
    Just used to work around a bug in an old libavcodec encoder version.
80
    Don't optimize them.
81 a552591f Michael Niedermayer
82 7d67aa9b Michael Niedermayer
tpel_mc_func {put,avg}_tpel_pixels_tab
83 8ea9ce41 Diego Biurrun
    Used only for SVQ3, so only optimize them if you need fast SVQ3 decoding.
84 7d67aa9b Michael Niedermayer
85 a552591f Michael Niedermayer
add_bytes/diff_bytes
86 8ea9ce41 Diego Biurrun
    For huffyuv only, optimize if you want a faster ffhuffyuv codec.
87 a552591f Michael Niedermayer
88
get_pixels / diff_pixels
89 8ea9ce41 Diego Biurrun
    Used for encoding, easy.
90 38aca760 Diego Biurrun
91 a552591f Michael Niedermayer
clear_blocks
92 8ea9ce41 Diego Biurrun
    easiest to optimize
93 38aca760 Diego Biurrun
94 a552591f Michael Niedermayer
gmc
95 8ea9ce41 Diego Biurrun
    Used for MPEG-4 gmc.
96
    Optimizing this should have a significant effect on the gmc decoding
97 2e1ad4a2 Loren Merritt
    speed.
98 a552591f Michael Niedermayer
99 143cc725 Michael Niedermayer
gmc1
100 8ea9ce41 Diego Biurrun
    Used for chroma blocks in MPEG-4 gmc with 1 warp point
101
    (there are 4 luma & 2 chroma blocks per macroblock, so
102 38aca760 Diego Biurrun
    only 1/3 of the gmc blocks use this, the other 2/3
103
    use the normal put_pixel* code, but only if there is
104 8ea9ce41 Diego Biurrun
    just 1 warp point).
105
    Note: DivX5 gmc always uses just 1 warp point.
106 143cc725 Michael Niedermayer
107 a552591f Michael Niedermayer
pix_sum
108 8ea9ce41 Diego Biurrun
    Used for encoding.
109 38aca760 Diego Biurrun
110 8c55915b Michael Niedermayer
hadamard8_diff / sse / sad == pix_norm1 / dct_sad / quant_psnr / rd / bit
111 8ea9ce41 Diego Biurrun
    Specific compare functions used in encoding, it depends upon the
112
    command line switches which of these are used.
113
    Don't waste your time with dct_sad & quant_psnr, they aren't
114
    really useful.
115 a552591f Michael Niedermayer
116
put_pixels_clamped / add_pixels_clamped
117 8ea9ce41 Diego Biurrun
    Used for en/decoding in the IDCT, easy.
118
    Note, some optimized IDCTs have the add/put clamped code included and
119
    then put_pixels_clamped / add_pixels_clamped will be unused.
120 a552591f Michael Niedermayer
121
idct/fdct
122 38aca760 Diego Biurrun
    idct (encoding & decoding)
123
    fdct (encoding)
124
    difficult to optimize
125
126 a552591f Michael Niedermayer
dct_quantize_trellis
127 8ea9ce41 Diego Biurrun
    Used for encoding with trellis quantization.
128 38aca760 Diego Biurrun
    difficult to optimize
129 a552591f Michael Niedermayer
130
dct_quantize
131 8ea9ce41 Diego Biurrun
    Used for encoding.
132 38aca760 Diego Biurrun
133 a552591f Michael Niedermayer
dct_unquantize_mpeg1
134 8ea9ce41 Diego Biurrun
    Used in MPEG-1 en/decoding.
135 a552591f Michael Niedermayer
136
dct_unquantize_mpeg2
137 8ea9ce41 Diego Biurrun
    Used in MPEG-2 en/decoding.
138 a552591f Michael Niedermayer
139
dct_unquantize_h263
140 8ea9ce41 Diego Biurrun
    Used in MPEG-4/H.263 en/decoding.
141 a552591f Michael Niedermayer
142
FIXME remaining functions?
143 8ea9ce41 Diego Biurrun
BTW, most of these functions are in dsputil.c/.h, some are in mpegvideo.c/.h.
144 a552591f Michael Niedermayer
145
146 38aca760 Diego Biurrun
147 a552591f Michael Niedermayer
Alignment:
148 8ea9ce41 Diego Biurrun
Some instructions on some architectures have strict alignment restrictions,
149 c5a44f57 Diego Biurrun
for example most SSE/SSE2 instructions on x86.
150 8ea9ce41 Diego Biurrun
The minimum guaranteed alignment is written in the .h files, for example:
151 a552591f Michael Niedermayer
    void (*put_pixels_clamped)(const DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size);
152
153
154 7b8c3aed Michael Niedermayer
General Tips:
155
-------------
156
Use asm loops like:
157 be449fca Diego Pettenò
__asm__(
158 7b8c3aed Michael Niedermayer
    "1: ....
159
    ...
160
    "jump_instruciton ....
161 8144dff0 Michael Niedermayer
Do not use C loops:
162 7b8c3aed Michael Niedermayer
do{
163 be449fca Diego Pettenò
    __asm__(
164 7b8c3aed Michael Niedermayer
        ...
165
}while()
166
167 be449fca Diego Pettenò
Use __asm__() instead of intrinsics. The latter requires a good optimizing compiler
168 7b8c3aed Michael Niedermayer
which gcc is not.
169
170 a552591f Michael Niedermayer
171
Links:
172 5e123bd3 Michael Niedermayer
======
173 3df7be0f Michael Niedermayer
http://www.aggregate.org/MAGIC/
174
175 8ea9ce41 Diego Biurrun
x86-specific:
176 5e123bd3 Michael Niedermayer
-------------
177 a552591f Michael Niedermayer
http://developer.intel.com/design/pentium4/manuals/248966.htm
178
179 38aca760 Diego Biurrun
The IA-32 Intel Architecture Software Developer's Manual, Volume 2:
180 a552591f Michael Niedermayer
Instruction Set Reference
181
http://developer.intel.com/design/pentium4/manuals/245471.htm
182
183
http://www.agner.org/assem/
184
185
AMD Athlon Processor x86 Code Optimization Guide:
186
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pdf
187
188 20e570c8 Guillaume Poirier
189
ARM-specific:
190 5e123bd3 Michael Niedermayer
-------------
191 14c2634b Guillaume Poirier
ARM Architecture Reference Manual (up to ARMv5TE):
192
http://www.arm.com/community/university/eulaarmarm.html
193
194
Procedure Call Standard for the ARM Architecture:
195
http://www.arm.com/pdfs/aapcs.pdf
196
197
Optimization guide for ARM9E (used in Nokia 770 Internet Tablet):
198
http://infocenter.arm.com/help/topic/com.arm.doc.ddi0240b/DDI0240A.pdf
199
Optimization guide for ARM11 (used in Nokia N800 Internet Tablet):
200
http://infocenter.arm.com/help/topic/com.arm.doc.ddi0211j/DDI0211J_arm1136_r1p5_trm.pdf
201
Optimization guide for Intel XScale (used in Sharp Zaurus PDA):
202
http://download.intel.com/design/intelxscale/27347302.pdf
203 1a592ecc Dmitry Antipov
Intel Wireless MMX2 Coprocessor: Programmers Reference Manual
204
http://download.intel.com/design/intelxscale/31451001.pdf
205 20e570c8 Guillaume Poirier
206 2c2b3130 Luca Barbato
PowerPC-specific:
207 5e123bd3 Michael Niedermayer
-----------------
208 a1d0b6a2 Diego Biurrun
PowerPC32/AltiVec PIM:
209 2c2b3130 Luca Barbato
www.freescale.com/files/32bit/doc/ref_manual/ALTIVECPEM.pdf
210
211 a1d0b6a2 Diego Biurrun
PowerPC32/AltiVec PEM:
212 2c2b3130 Luca Barbato
www.freescale.com/files/32bit/doc/ref_manual/ALTIVECPIM.pdf
213
214
CELL/SPU:
215
http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/30B3520C93F437AB87257060006FFE5E/$file/Language_Extensions_for_CBEA_2.4.pdf
216
http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/9F820A5FFA3ECE8C8725716A0062585F/$file/CBE_Handbook_v1.1_24APR2007_pub.pdf
217 20e570c8 Guillaume Poirier
218 277bb936 Michael Niedermayer
SPARC-specific:
219 5e123bd3 Michael Niedermayer
---------------
220 277bb936 Michael Niedermayer
SPARC Joint Programming Specification (JPS1): Commonality
221
http://www.fujitsu.com/downloads/PRMPWR/JPS1-R1.0.4-Common-pub.pdf
222
223 777bbfdd Michael Niedermayer
UltraSPARC III Processor User's Manual (contains instruction timings)
224
http://www.sun.com/processors/manuals/USIIIv2.pdf
225
226 71253ce9 Dominik Mierzejewski
VIS Whitepaper (contains optimization guidelines)
227
http://www.sun.com/processors/vis/download/vis/vis_whitepaper.pdf
228 277bb936 Michael Niedermayer
229 a552591f Michael Niedermayer
GCC asm links:
230 5e123bd3 Michael Niedermayer
--------------
231 3df7be0f Michael Niedermayer
official doc but quite ugly
232
http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
233
234 8ea9ce41 Diego Biurrun
a bit old (note "+" is valid for input-output, even though the next disagrees)
235 8c55915b Michael Niedermayer
http://www.cs.virginia.edu/~clc5q/gcc-inline-asm.pdf