Re: Question regarding pthread_cond_wait/pthread_cond_signal latencies

[Pedro Gonnet <gonnet@maths.ox.ac.uk>]

On Sat, 2011-05-21 at 16:48 -0400, Mark Hounschell wrote:
> On 05/20/2011 06:08 AM, Pedro Gonnet wrote:
> >
> > Hi guys,
> >
> > I'm currently working on a shared-memory parallel Molecular Dynamics
> > simulation library (http://mdcore.sourceforge.net/) geared towards
> > multi-core systems.
> >
> > The library uses pthreads (plus some OpenMP for some simple loops) and
> > uses pthread_cond_wait and pthread_cond_signal to coordinate a group of
> > worker threads.
> >
> > I've been profiling the library on different machines and kernels and
> > have noticed that in many cases there are significant (several ms,
> > measured with Intel's Vtune-thing) lags between calls to
> > pthread_cond_signal and the waiting thread actually getting back to
> > work.
> >
> > I've tried the Ubuntu -rt and -preempt kernels, and the whole simulation
> > runs twice as slowly, despite following the advice given here:
> >
> >          https://rt.wiki.kernel.org/index.php/HOWTO:_Build_an_RT-application
> >
> > My question is the following: which kernel (or set of configuration
> > options) will minimize these latencies? And if linux-rt is the answer,
> > in what ways do I have to be careful when porting the simulation for
> > this kernel?
> >
> 
> Are you saying several ms latency from pthread_cond_signal to waking up a 
> thread in pthread_cond_wait?
> 

Yes. Or at least, this is what Vtune says. It could also be a fluke in
Vtune, but I would still be interested in knowing what kernel or what
kernel options can make these operations as fast as possible.

Cheers, Pedro