Based on discussions on the svn-src mailing list, rework r218195:

 - entirely eliminate some calls to uio_yeild() as being unnecessary,
   such as in a sysctl handler.

 - move should_yield() and maybe_yield() to kern_synch.c and move the
   prototypes from sys/uio.h to sys/proc.h

 - add a slightly more generic kern_yield() that can replace the
   functionality of uio_yield().

 - replace source uses of uio_yield() with the functional equivalent,
   or in some cases do not change the thread priority when switching.

 - fix a logic inversion bug in vlrureclaim(), pointed out by bde@.

 - instead of using the per-cpu last switched ticks, use a per thread
   variable for should_yield().  With PREEMPTION, the only reasonable
   use of this is to determine if a lock has been held a long time and
   relinquish it.  Without PREEMPTION, this is essentially the same as
   the per-cpu variable.

1 files changed, 2 insertions, 24 deletions

diff --git a/sys/kern/subr_uio.c b/sys/kern/subr_uio.c
index 96f9331..934a533 100644
--- a/sys/kern/subr_uio.c
+++ b/sys/kern/subr_uio.c
@@ -352,33 +352,11 @@ again:
 	return (0);
 }
 
-int
-should_yield(void)
-{
-
-	return (ticks - PCPU_GET(switchticks) >= hogticks);
-}
-
-void
-maybe_yield(void)
-{
-
-	if (should_yield())
-		uio_yield();
-}
-
 void
 uio_yield(void)
 {
-	struct thread *td;
-
-	td = curthread;
-	DROP_GIANT();
-	thread_lock(td);
-	sched_prio(td, td->td_user_pri);
-	mi_switch(SW_INVOL | SWT_RELINQUISH, NULL);
-	thread_unlock(td);
-	PICKUP_GIANT();
+
+	kern_yield(curthread->td_user_pri);
 }
 
 int