Re: [PATCH 0/4] faster gnulib-tool

[Pádraig Brady]

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.