"What speedup justifies an optimization" section

Originally committed as revision 11595 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/optimization.txt

@@ -23,6 +23,15 @@ and how they can be optimized.
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+What speedup justifies an optimizetion?
+Normaly with clean&simple optimizations and widely used codecs a overall
+speedup of the affected codec of 0.1% is enough. These speedups accumulate
+and can make a big difference after a while ...
+Also if none of the following gets worse and at least one gets better then an
+optimization is always a good idea even if the overall gain is less than 0.1%
+(speed, binary code size, source size, source readability)
+For obscure codecs noone uses, the goal is more toward keeping the code clean
+small and readable than to make it 1% faster.
 
 
 WTF is that function good for ....: