K 10
svn:author
V 3
jhb
K 8
svn:date
V 27
2007-10-27T22:07:40.000000Z
K 7
svn:log
V 633
Change the roundrobin implementation in the 4BSD scheduler to trigger a
userland preemption directly from hardclock() via sched_clock() when a
thread uses up a full quantum instead of using a periodic timeout to cause
a userland preemption every so often.  This fixes a potential deadlock
when IPI_PREEMPTION isn't enabled where softclock blocks on a lock held
by a thread pinned or bound to another CPU.  The current thread on that
CPU will never be preempted while softclock is blocked.

Note that ULE already drives its round-robin userland preemption from
sched_clock() as well and always enables IPI_PREEMPT.

MFC after:	1 week

END