sched/deadline: Fix confusing comments about selection of top pi-waiter

This comment in the code is incomplete, and I believe it begs a definition of
dl_boosted to make sense of the condition that follows. Rewrite the comment and
also rearrange the condition that follows to reflect the first condition "we
have a top pi-waiter which is a SCHED_DEADLINE task" in that order. Also fix a
typo that follows.

Signed-off-by: Joel Fernandes <joelaf@google.com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Acked-by: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170713022429.10307-1-joelaf@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a84299f44b5d8c2990e10f9a74d1818fad3a7040..755bd3f1a1a93a8f1daf713dd36578637ce515c5 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1392,17 +1392,19 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
        struct sched_dl_entity *pi_se = &p->dl;
 
        /*
-        * Use the scheduling parameters of the top pi-waiter
-        * task if we have one and its (absolute) deadline is
-        * smaller than our one... OTW we keep our runtime and
-        * deadline.
+        * Use the scheduling parameters of the top pi-waiter task if:
+        * - we have a top pi-waiter which is a SCHED_DEADLINE task AND
+        * - our dl_boosted is set (i.e. the pi-waiter's (absolute) deadline is
+        *   smaller than our deadline OR we are a !SCHED_DEADLINE task getting
+        *   boosted due to a SCHED_DEADLINE pi-waiter).
+        * Otherwise we keep our runtime and deadline.
         */
-       if (pi_task && p->dl.dl_boosted && dl_prio(pi_task->normal_prio)) {
+       if (pi_task && dl_prio(pi_task->normal_prio) && p->dl.dl_boosted) {
                pi_se = &pi_task->dl;
        } else if (!dl_prio(p->normal_prio)) {
                /*
                 * Special case in which we have a !SCHED_DEADLINE task
-                * that is going to be deboosted, but exceedes its
+                * that is going to be deboosted, but exceeds its
                 * runtime while doing so. No point in replenishing
                 * it, as it's going to return back to its original
                 * scheduling class after this.