-P sets parallelism, -n number of arguments for each execution. Those are my main weapons. (-i is usually also necessary, and can allow for some pretty creative situations)

I don't swear on HN, but Holy Shit, I just added -P to xargs in a testsuite bash script, and it's 7 times faster.

I only have quad core, but -P values higher than 4 give better performance. Maybe because the tests take different amounts of time, and it avoids them backing up. To get x7, I had -P equal to the number of tests.

If the tests are ever waiting for I/O or something, or otherwise using less than one full CPU core, then I think that could explain why running more than the number of cores would be an improvement. If you run "top", or use the "time" utility, what fraction of a CPU core does each test use?

Good thinking, but they don't do any file io, and I'm not sure how it could use less than a full CPU (wouldn't it just finish sooner? Though waiting for io could do that). OTOH it's java (on android, so dex format) and does some classloading of user classes... so maybe that is io? Here's time results:

  real    0m1.818s
  user    0m2.020s
  sys     0m0.900s

top. (It completes in 1 sec, so put in a while loop - BTW top isn't behaving normally, "1" not giving multiple CPUs and not fitting on screen). Jus the top line:

  User 51%, System 23%, IOW 0%, IRQ 0%

It does. What xargs can't do is run stuff in parallel across many machines.

Yeah, you'd have to combine it with something like

https://github.com/erikfrey/bashreduce

Or pssh

It can, check the -n and -P arguments.

xargs can do both and it rocks. https://www.google.com/search?q=xargs+parallel