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

[Michael Dickens]

On May 22, 2007, at 11:46 PM, Eric Blossom wrote:
> pthread_attr_setschedpolicy is not the same thing as
> sched_setscheduler.  It's for setting up the attribute that is passed
> pthread_create.

Touché.  Thanks for pointing that out ... should have been  
"pthread_setschedparam()" instead.  This routine is, if I'm reading  
the MAN pages correctly, an exact parallel to "sched_setscheduler()",  
but in pthread terms.  Here's the basic code:

-------
  int policy = SCHED_FIFO
  pthread_t this_thread = pthread_self ();
  int priority = (sched_get_priority_max (policy) +
                  sched_get_priority_min (policy)) / 2;
  struct sched_param param;
  memset (&param, 0, sizeof (param));
  param.sched_priority = priority;
  int result = pthread_setschedparam (this_thread, policy, &param)
  if  (result != 0) {
    printf ("Error %d doing 'pthread_setschedparam'.\n", errno);
    ...
-------
Compare that with "gr_realtime.cc":
----
  int policy = SCHED_FIFO;
  int pri = (sched_get_priority_max (policy) +  
sched_get_priority_min (policy)) / 2;
  int pid = 0;  // this process

  struct sched_param param;
  memset(&param, 0, sizeof(param));
  param.sched_priority = pri;
  int result = sched_setscheduler(pid, policy, &param);
  if (result != 0){
    ....
--------
You'll notice that the 2 differences are (1) having to get the  
current pthread instead of the PID; and (2) using  
"pthread_setschedparam()" instead of "sched_setscheduler()".

Interestingly, at least on OSX 10.4.9, all policies have a (min,max)  
priority of (15,47), and the default for any process is the mid-point  
(31).  Thus for OSX, "real time" priority needs to be closer to the  
MAX than the mid-point.  The default policy is "Other" (1), whatever  
that is.

But, again, for some reason 'configure' isn't registering that  
pthreads are available on OSX 10.4 ... which they clearly are. - MLD