linux-kernel - [PATCH AUTOSEL 5.2 095/123] sched/psi: Reduce psimon FIFO priority

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Date:   Tue, 13 Aug 2019 22:10:19 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.2 095/123] sched/psi: Reduce psimon FIFO priority

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit 14f5c7b46a41a595fc61db37f55721714729e59e ]

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: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Tested-by: Suren Baghdasaryan <surenb@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/sched/psi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7acc632c3b82b..7fe2c5fd26b54 100644
--- a/kernel/sched/psi.c
+++ b/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;
 
-- 
2.20.1