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Re: [Discuss-gnuradio] End-to-end delay question

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] End-to-end delay question
Date: Tue, 22 May 2007 20:46:00 -0700
User-agent: Mutt/1.5.9i

On Tue, May 22, 2007 at 10:59:22AM -0400, Michael Dickens wrote:
> On May 22, 2007, at 12:28 AM, Eric Blossom wrote:
> >The priority is set to the midpoint of the FIFO range, not maximized.
> My bad on the "maximized" ... but ... ummm ... no, not the midpoint  
> either the way it's written, if I understand the function calls  
> correctly.  Here's the line:
>   int pri = (sched_get_priority_max (policy) -  
> sched_get_priority_min (policy)) / 2;
> The midpoint would be (... + ...) / 2.  ;)

Thanks.  Fixed in the trunk.

> >I don't think we want to be creating new threads just to try
> >to set real time scheduling.
> These changes are made to the current running thread, not to a new  
> thread, just like the code in "gr_realtime.cc".  IMHO GNU Radio  
> already has enough threads, especially on OSX's implementation  
> because of Apple's weirdness of requiring separate threads for  
> callbacks on Audio and USB.
> >I strongly suspect that if a pthread
> >implementation supports pthread_attr_setschedpolicy with SCHED_RR or
> >SCHED_FIFO, then they will also implement sched_setscheduler with
> On OSX 10.4.9 (and, I would presume any 10.4.X):  
> sched_get_priority_max(), sched_get_priority_min (), SCHED_FIFO, and  
> "struct sched_param" [and "struct sched_param".sched_priority] are  
> defined in standard header files in /usr/include and seem to work as  
> required for modifying the scheduling priority and policy.   
> Strangely, the only part that's missing from headers is  
> sched_setscheduler() ... which gets divided and renamed to  
> pthread_attr_setschedpolicy() and pthread_attr_setschedparam().

pthread_attr_setschedpolicy is not the same thing as
sched_setscheduler.  It's for setting up the attribute that is passed
pthread_create.  The friendly manual says:

       pthread_attr_getschedpolicy,  pthread_attr_setschedpolicy - get and set
       the schedpolicy attribute (REALTIME THREADS)


       After  these attributes have been set, a thread can be created with the
       specified attributes using pthread_create(). Using these routines  does
       not affect the current running thread.


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