linux-kernel - [PATCH 1/5] sched/pci: Reduce psimon FIFO priority

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Message-Id: <20190801111541.685367413@infradead.org>
Date:   Thu, 01 Aug 2019 13:13:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        Suren Baghdasaryan <surenb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 1/5] sched/pci: Reduce psimon FIFO priority

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.

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

--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1051,7 +1051,7 @@ struct psi_trigger *psi_trigger_create(s
 
 	if (!rcu_access_pointer(group->poll_kworker)) {
 		struct sched_param param = {
-			.sched_priority = MAX_RT_PRIO - 1,
+			.sched_priority = 1,
 		};
 		struct kthread_worker *kworker;