Re: bsdcpio and bsdtar installed by default

["Greg A. Woods; Planix, Inc." <woods%planix.ca@localhost>]

On 5-Jun-08, at 1:56 PM, Joerg Sonnenberger wrote:
> For gzip/libz based compression, I think the overhead of pipe is  
> clearly
> as large as the gain from running on different cores (e.g. sharing L2
> caches).

That may be a problem with pipes then, perhaps.

> For bzip2 the ratio changes somewhat, but it seems like the
> overhead due to pipe usage and the additional cache trashing are  
> mostly
> compensating each other.
>
> For my Core2 laptop (hw.ncpu=2):
>
> bsdtar xf libX11-1.1.3.tar.bz2
> 1.18s user 0.12s system 99% cpu 1.305 total
>
> bsdtar --use-compress-program /usr/bin/bunzip2 -xf  
> libX11-1.1.3.tar.bz2
> 1.25s user 0.16s system 109% cpu 1.285 total

Those numbers don't quite make sense to me.  Something looks (a little  
bit) wrong.  The results seem to indicate the combined CPU use  
exceeded that possible by one CPU alone.  There also seems to be a  
tiny savings in wall clock time too.  However the user time is higher  
than I would expect for the overhead of reading and writing through a  
pipe (from user-land alone).

> The former uses internal lbibz2 handling, the second call uses the
> external program. Both cases to tmpfs. So while it is slightly  
> faster to
> use the external program, it means 10% more over all resource usage.

I would expect a small amount of resource usage overhead, but 10% does  
seem high.

What most concerns me here is the time spent in user-land -- it would  
be interesting to profile both processes in the 2nd case to see where  
the overhead really is.

> For extraction to a real file system, the situation will change  
> somewhat
> as the operations are generally IO bound in that case.


Indeed.

--
                                        Greg A. Woods; Planix, Inc.
                                        <woods%planix.ca@localhost>