Re: Question regarding pthread_cond_wait/pthread_cond_signal latencies

[Armin Steinhoff <armin@steinhoff.de>]

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.

At what priority are the worker threads running ?

In order to schedule these threads by the real-time part of the CFS 
scheduler they should run at lest at a priority of 20 (rt_sched_class)

Regards

--Armin


> 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?
>
> Cheers and thanks,
> Pedro
>
>
>
>
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