kern_yield vs ukbd_yield

[Andriy Gapon]

on 11/12/2011 23:48 mdf at FreeBSD.org said the following:
> On Sun, Dec 11, 2011 at 1:12 PM, Andriy Gapon <avg at freebsd.org> wrote:
>>
>> Does the following change do what I think that it does?
>> Thank you!
>>
>> Author: Andriy Gapon <avg at icyb.net.ua>
>> Date:   Thu Sep 1 16:50:13 2011 +0300
>>
>>    ukbd: drop local duplicate of kern_yield and use that instead
>>
>> diff --git a/sys/dev/usb/input/ukbd.c b/sys/dev/usb/input/ukbd.c
>> index 086c178..8078cbb 100644
>> --- a/sys/dev/usb/input/ukbd.c
>> +++ b/sys/dev/usb/input/ukbd.c
>> @@ -399,33 +399,6 @@ ukbd_put_key(struct ukbd_softc *sc, uint32_t key)
>>  }
>>
>>  static void
>> -ukbd_yield(void)
>> -{
>> -       struct thread *td = curthread;
>> -       uint32_t old_prio;
>> -
>> -       DROP_GIANT();
>> -
>> -       thread_lock(td);
>> -
>> -       /* get current priority */
>> -       old_prio = td->td_base_pri;
>> -
>> -       /* set new priority */
>> -       sched_prio(td, td->td_user_pri);
>> -
>> -       /* cause a task switch */
>> -       mi_switch(SW_INVOL | SWT_RELINQUISH, NULL);
>> -
>> -       /* restore priority */
>> -       sched_prio(td, old_prio);
>> -
>> -       thread_unlock(td);
>> -
>> -       PICKUP_GIANT();
>> -}
>> -
>> -static void
>>  ukbd_do_poll(struct ukbd_softc *sc, uint8_t wait)
>>  {
>>
>> @@ -439,7 +412,7 @@ ukbd_do_poll(struct ukbd_softc *sc, uint8_t wait)
>>                while (sc->sc_inputs == 0) {
>>
>>                        /* give USB threads a chance to run */
>> -                       ukbd_yield();
>> +                       kern_yield(-1);
> 
> Not quite.
> 
> 1) -1 should be spelled PRI_UNCHANGED, except ukbd_yield() uses
> td_user_pri, but then puts it back again, so I think UNCHANGED is what
> is meant.
> 2) kern_yield() calls it a SW_VOL rather than SW_INVOL, which seems
> the desired behaviour here anyways, since this is an explicit (i.e.
> voluntary) yield.

Thank you for the explanation.  So would you say that the patch is OK?

-- 
Andriy Gapon