GNU Parallel - build and execute command lines from standard input in parallel(savannah.gnu.org)
savannah.gnu.org
GNU Parallel - build and execute command lines from standard input in parallel
http://savannah.gnu.org/projects/parallel
11 comments
This is very cool, but a little opaque at first read... To get a quicker and digestible intro, watch the video introduction (linked on the page): http://www.youtube.com/watch?v=OpaiGYxkSuQ
Well, the example(at least the first one) in that video is bit skewed. First, he runs gzip and then immediately runs 'parallel gzip' without dropping disk caches. So in the later case the bottleneck would be CPU rather than disk IO(everything read from disk cache in the RAM). IMO I expect for the work that is IO bound we won't see any significant improvement using parallel or anything similar.
Ideas for next video are most welcome. The ideal task:
1. Is single threaded 2. Takes a lot of CPU 3. Is a task that everyone can understand and relate to and which is close to a real world scenario
I have loads of examples meeting requirement 1+2. It is 3 that is the hard part.
Post them to [email protected]
1. Is single threaded 2. Takes a lot of CPU 3. Is a task that everyone can understand and relate to and which is close to a real world scenario
I have loads of examples meeting requirement 1+2. It is 3 that is the hard part.
Post them to [email protected]
How about doing something with imagemagick or mencoder? I think video encoding/decoding gives a nice balance between disk and cpu usage.
Here's an imagemagick example; over six minutes with xargs, under 20 seconds with parallel
$ ls *.png |wc -l
3580
$ time ls|sed 's/\(.*\)\..*/\1/'|parallel convert {}.png {}.ppm
ls --color 0.00s user 0.01s system 63% cpu 0.016 total
sed 's/\(.*\)\..*/\1/' 0.01s user 0.00s system 39% cpu 0.025 total
parallel convert {}.png {}.ppm 97.39s user 61.87s system 890% cpu 17.883 total
$ time ls|sed 's/\(.*\)\..*/\1/'|xargs -I {} convert {}.png {}.ppm
ls --color 0.01s user 0.00s system 63% cpu 0.016 total
sed 's/\(.*\)\..*/\1/' 0.01s user 0.00s system 39% cpu 0.025 total
xargs -I {} convert {}.png {}.ppm 93.08s user 47.88s system 38% cpu 6:10.88 totalJust tried it and got errors galore. Oh well, I'll keep trying.
Make sure you are using GNU Parallel and not another version of parallel. Try:
parallel --version
parallel --version
In what ways is this better than make -j?
Because it can be run on the command line, ad hoc. Make -j is great for pre-existing command lists and dependencies. But as the man page describes, parallel is like xargs, which I use all the time on the command line for ad hoc actions (frees me from having to write a bash loop).
make requires a Makefile, whereas one can pass parameters directly to parallel.
There also seems to be a few more options revolving around job success/failure and how to react -- a) ignore failed jobs and report how many at the end, b) cleanly exit as soon as a job fails and c) stop all jobs as soon as one fails.
There also seems to be a few more options revolving around job success/failure and how to react -- a) ignore failed jobs and report how many at the end, b) cleanly exit as soon as a job fails and c) stop all jobs as soon as one fails.
Those (a) (b) and (c) points sound like strengths of make, to me.
Sorry, those were features of parallel, not make (unless I'm mistaken).
It seems like 90% of the uses for this can be taken care of with xargs:
echo "file1 file2" | xargs -P 2 gzipAs I understand it, xargs only runs on the local machine; GNU parallel can run on remote machines as well. So parallel is the cluster-friendly version of xargs's -P.
Yep. There also is dxargs which looks very useful
http://www.semicomplete.com/blog/geekery/distributed-xargs.h...
Please read http://www.gnu.org/software/parallel/man.html#differences_be... before selecting dxargs.
Please read http://www.gnu.org/software/parallel/man.html#differences_be... before selecting xargs.
Don't you need
echo "file1 file2" | xargs -P2 -n1 gzip
?Probably, although it doesn't seem to be the focus of xargs.
And the version of xargs that is included with Solaris 10 doesn't have the -P option. In which case, installing gnu parallel is a slightly easier option than installing a different version of xargs.
And the version of xargs that is included with Solaris 10 doesn't have the -P option. In which case, installing gnu parallel is a slightly easier option than installing a different version of xargs.
See also the 'push' shell: http://code.google.com/p/push/
On first impressions I like this much more than ppss. The distributed setup is much easier and the documentation is more thorough.
I'll express here what I feel while reading any man pages..
Examples should be at the top!
(10 years of frustration in that one line message :p)
Examples should be at the top!
(10 years of frustration in that one line message :p)
I've just resigned to do a search for /EXAMPLES as soon as I need any.
LESS='+/EXAMPLE' man parallel
Ah, one of these again.
I wrote a simpler one a couple of years ago (http://code.google.com/p/spawntool/) myself. All it does is read commands from stdin, one per line, and keep a desired number of processes running until all command lines are exhausted. Simple.
I wrote my own because I got tired of all kinds of substitution and quoting issues with xargs. With spawn I only need to generate the shell commands and instead of piping them to bash I pipe them to spawn. Also, this means I can easily review your command line generation with less (so that quotes etc. are good) until I eventually switch to sh or spawn.
I wrote a simpler one a couple of years ago (http://code.google.com/p/spawntool/) myself. All it does is read commands from stdin, one per line, and keep a desired number of processes running until all command lines are exhausted. Simple.
I wrote my own because I got tired of all kinds of substitution and quoting issues with xargs. With spawn I only need to generate the shell commands and instead of piping them to bash I pipe them to spawn. Also, this means I can easily review your command line generation with less (so that quotes etc. are good) until I eventually switch to sh or spawn.
If it is simple I would love to see the examples from http://www.gnu.org/software/parallel/man.html#example__worki... converted to spawn.
Nice example from the docs:
Convert .mp3 to .ogg running one process per CPU core on local computer and server2:
Convert .mp3 to .ogg running one process per CPU core on local computer and server2:
parallel --trc {.}.ogg -j+0 -S server2,: \ 'mpg321 -w - {} | oggenc -q0 - -o {.}.ogg' ::: *.mp3Someone managed to get this working on os x?
Standard "./configure && make && make install" outputs errors.
Standard "./configure && make && make install" outputs errors.
The MacPorts version worked for me.
Perhaps the Portfile will have the patches you need to manually compile on OS X:
http://trac.macports.org/browser/trunk/dports/sysutils/paral...
Perhaps the Portfile will have the patches you need to manually compile on OS X:
http://trac.macports.org/browser/trunk/dports/sysutils/paral...