Reduce umtx-related work on exec and exit

- there is no need to take the process lock to iterate the thread
  list after single-threading is enforced
- typically there are no mutexes to clean up (testable without taking
  the global umtx lock)
- typically there is no need to adjust the priority (testable without
  taking thread lock)

Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D20160

1 files changed, 21 insertions, 0 deletions

diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c
index a85356107930..c53b838f8db6 100644
--- a/sys/kern/sched_4bsd.c
+++ b/sys/kern/sched_4bsd.c
@@ -930,6 +930,27 @@ sched_lend_user_prio(struct thread *td, u_char prio)
 		td->td_flags |= TDF_NEEDRESCHED;
 }
 
+/*
+ * Like the above but first check if there is anything to do.
+ */
+void
+sched_lend_user_prio_cond(struct thread *td, u_char prio)
+{
+
+	if (td->td_lend_user_pri != prio)
+		goto lend;
+	if (td->td_user_pri != min(prio, td->td_base_user_pri))
+		goto lend;
+	if (td->td_priority >= td->td_user_pri)
+		goto lend;
+	return;
+
+lend:
+	thread_lock(td);
+	sched_lend_user_prio(td, prio);
+	thread_unlock(td);
+}
+
 void
 sched_sleep(struct thread *td, int pri)
 {