Paolo Bonzini wrote: > > A while ago I made a lot of timings regarding the speed of various shell > constructs; you can find them on the Autoconf list. Here are the > relevant ones: > > $ time sh -c 'for i in `seq 1 1000`; do :; done' > user 0m0.034s > sys 0m0.024s > > $ time sh -c 'for i in `seq 1 1000`; do (:); done' > user 0m0.486s > sys 0m2.377s > > $ time sh -c 'for i in `seq 1 1000`; do echo abc | :; done' > user 0m0.958s > sys 0m4.657s > > echo and : are shell builtins, but they fork, so they're slow. s/:/sed/ > and you see my point. > > If this 10x-30x improvement affected 20% of the shell execution time, > one could expect a decent speedup. > > That would probably amount to a rewrite of bash, dash, or whatever else. > You would have to make the main shell loop centered around > event-driven processing of file descriptors, to provide all the pipes > with a single process. > > A fun project, but probably not one that I or anyone else will attempt > without funding. :-)
Nice info thanks. I tested stuff like this previously, and found it highly shell dependent: http://www.pixelbeat.org/programming/shell_script_mistakes.html#performance In summary I noticed that dash forked twice as fast as bash, and dash's base looping speed was 6 times faster. cheers, Pádraig.
