sched/psi: Reduce psimon FIFO priority

commit 14f5c7b46a41a595fc61db37f55721714729e59e upstream.

PSI defaults to a FIFO-99 thread, reduce this to FIFO-1.

FIFO-99 is the very highest priority available to SCHED_FIFO and
it not a suitable default; it would indicate the psi work is the
most important work on the machine.

Since Real-Time tasks will have pre-allocated memory and locked it in
place, Real-Time tasks do not care about PSI. All it needs is to be
above OTHER.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Tested-by: NSuren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>

kernel/sched/psi.c

@@ -1051,7 +1051,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
 
 	if (!rcu_access_pointer(group->poll_kworker)) {
 		struct sched_param param = {
-			.sched_priority = MAX_RT_PRIO - 1,
+			.sched_priority = 1,
 		};
 		struct kthread_worker *kworker;