Re: Question regarding pthread_cond_wait/pthread_cond_signal latencies

[Rolando Martins <rolando.martins@gmail.com>]

Hi guys,
I am building a real-time middleware and have also struggled with
similar behavior, at this point I reduced to the bare minimum the use
of condition variables.
(using 33-rt)

Rolando


On Sat, May 21, 2011 at 9:51 PM, Pedro Gonnet <gonnet@maths.ox.ac.uk> wrote:
> 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
>
>
>
>
>
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