dtrace discuss - May 2006 - A question about sched:::sleep and sched::wakeup

Hi, experts,

I use dtrace to monitor a thread.  I find it first sleeps on an object ( 
the thread uses select() to sleep 5ms)
and then it is enqueued into runnable queue.

I use a script to catch sched:::sleep, sched:::on-cpu sched:::off-cpu 
and sched:::wakeup
According to the dtrace manual, after sched:::sleep is fired, 
sched:::wakeup should also be fired
when the thread is waken up.

But sched:::wakeup is not fired and sched:::enqueue is fired instead?   
I don''t use any condition in "sched:::wakeup".

Does anyone know why?

Thanks

Brian

On Tue, May 02, 2006 at 04:13:30PM +0800, brian.lu
wrote:
> Hi, experts,
> 
> I use dtrace to monitor a thread.  I find it first sleeps on an object ( 
> the thread uses select() to sleep 5ms)
> and then it is enqueued into runnable queue.
> 
> I use a script to catch sched:::sleep, sched:::on-cpu sched:::off-cpu
> and sched:::wakeup According to the dtrace manual, after sched:::sleep
> is fired, sched:::wakeup should also be fired when the thread is waken
> up.
> 
> But sched:::wakeup is not fired and sched:::enqueue is fired instead?   
> I don''t use any condition in "sched:::wakeup".
> 
> Does anyone know why?
This looks like a bug;  cv_timedwait_sig()  (which is what the select() turns
into) sets up a timer to call setrun() on the thread when the timeout expires.
That turns into a cv_unsleep() call, which removes it from the queue and
sets it running, but never fires the sched:::wakeup call.

File a bug.

Cheers,
- jonathan

-- 
Jonathan Adams, Solaris Kernel Development