[Asterisk-Dev] Dev call 1.2 release discussion

[Steve Kann]

Kristian Nielsen wrote:

>Tzafrir Cohen <tzafrir.cohen at xorcom.com> writes:
>
>  
>
>>  It appears there's nothing much to do about that. Unless someone can
>>	suggest and code a useful userspace timing source, the problem is here
>>	to stay for a while
>>    
>>
>
>Is there anything more to it that a thread that does something like this:
>
>  struct pollfd fds[1];
>  for(;;) {
>    int timeout = ast_sched_wait(sched);
>    poll(fds, 0, timeout);
>    ast_sched_runq(sched);
>  }
>
>with appropriate handlers set up with ast_sched_add()? I guess there
>must be since it is a problem, so can anyone explain the issues?
>  
>

There's nothing really wrong with that -- it's how the scheduling queue 
is run in chan_iax2 right now, if you don't have zaptel (in the 
underlying implementation, anyway, where ast_io_wait() calls poll)..

The only thing is that when the system is busy, one can often sleep for 
much longer (i.e. 100 or 200ms) than you ask for, and the kernel may 
prefer to wake up a thread that's waiting on io and gets it, as opposed 
to a thread that's waiting on a timeout, and the timeout expires.

Running the threads with real-time priority, however, seems to be pretty 
reliable in causing the wakeup to happen on-time much more often.

-SteveK