ULE/yielding patch for testing.

[Daniel Eischen]

On Thu, 4 Oct 2007, Jeff Roberson wrote:

> On Thu, 4 Oct 2007, Daniel Eischen wrote:
>
>> On Thu, 4 Oct 2007, Jeff Roberson wrote:
>> 
>>> 
>>> I believe I have fixed this bug in the enclosed patch.  It is rooted from 
>>> /usr/src/sys so you should cd there to apply it.
>> 
>> This doesn't break realtime threads doing a sched_yield() does
>> it?  I couldn't easily see how the priority gets set back into
>> the realtime class range.  But then, maybe I'm a dummy ;-)
>
> Well the historical behavior was for sched_yield() to not adjust priorities. 
> It just requeues at the back of the queue for that priority. Xu changed this 
> in 7.0 but he didn't answer my mail as to why.  We have a yield() call that 
> does drop to the max timeshare priority, however, it doesn't seem to have a 
> man page.
>
> The code removed was this:
>
> -       if (td->td_pri_class == PRI_TIMESHARE)
> -               sched_prio(td, PRI_MAX_TIMESHARE);
>
>
> So it really only effected timesharing threads.

As I read the change, now it affects real-time (which is the
desired behavior since it is a POSIX real-time extension).
But it should have POSIX-defined behavior, which is to requeue
at the back of the queue for that priority.

-- 
DE