Date: Sun, 11 Dec 2011 13:48:38 -0800 From: mdf@FreeBSD.org To: Andriy Gapon <avg@freebsd.org> Cc: usb@freebsd.org, hackers@freebsd.org Subject: Re: kern_yield vs ukbd_yield Message-ID: <CAMBSHm-Gmyfm83wDnhKTWAM%2BM90SEdub9uNOexG7QvuGWvN3iQ@mail.gmail.com> In-Reply-To: <4EE51CB5.1060505@FreeBSD.org> References: <4EE51CB5.1060505@FreeBSD.org>
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On Sun, Dec 11, 2011 at 1:12 PM, Andriy Gapon <avg@freebsd.org> wrote:
>
> Does the following change do what I think that it does?
> Thank you!
>
> Author: Andriy Gapon <avg@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.
Thanks,
matthew
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