Author: Johan Melin
Date: 11:39:15 06/07/01
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On June 07, 2001 at 05:10:26, martin fierz wrote: >hi, > >this is from an earlier post of bob hyatt: > >>That is a basic optimization strategy... variables used close together in >>time should be close together in memory to take advantage of 32-byte line >>fills in cache. > >is this somthing which everybody is doing? is it worth the trouble to move >around variable declarations? if this is optimized, how much performance >gain can you expect compared to random variable placing? >are there any other strategies to optimize a program for good cache performance? >and how do you measure this, if ordering the variables in one function causes >that function to be 1% faster & the overall program 0.01% or something? just >so i can try it in one function for starters... Small, local variables in a function do not have cache problems. The problem is when you have large tables with data. Then you need to worry about how the data is organized. /Johan Melin >here's another observation i made: i have a P4 [i know... no need to tell me >that it's a bad choice :-)] desktop and a P3 laptop. i tried bobs recommendation >to use char and short arrays for small variables (like my >"lastbit" array), and on the P3 this was indeed faster - on the P4 it was >slower though. is this to be expected? > >cheers > martin
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