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Subject: Re: [OMPI devel] kernel 2.6.23 vs 2.6.24 - communication/wait times
From: Chris Samuel (chris_at_[hidden])
Date: 2010-04-11 20:48:16


On 10/04/10 15:12, Bogdan Costescu wrote:

> Have there been any process scheduler changes in the newer kernels ?

Are there ever kernels where that doesn't get tweaked ? ;-)

> I'm not sure that they could explain four orders of magnitude
> differences though...

One idea that comes to mind would be to run the child processes
under strace -c as that will monitor all the system calls and
report how long is spent in which. By running a comparison
with 2.6.23 and 2.6.24 then you might get a pointer to which
syscall(s) are taking longer.

Alternatively if you want to get fancy then you could play
with doing a git bisection between 2.6.23 and 2.6.24 to track
down the commit that introduces the regression.

To be honest it'd be interesting to see whether the issue still
manifests on a recent kernel though, if so then perhaps we might
be able to get the kernel developers interested (though they will
likely ask for a bisection too).

cheers!
Chris

-- 
  Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC