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Date:   Thu, 10 Jan 2019 11:12:32 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1 3/3] drivers/tty: increase priority for tty_buffer_worker

sched_priority = 1 is enough to dramatically reduce latency
on have system load produced by tasks with default user space prio.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/tty/tty_buffer.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 18bd7f48a319..7cf42f6570a0 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -13,11 +13,13 @@
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/sched/rt.h>
 #include <linux/wait.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/ratelimit.h>
+#include <uapi/linux/sched/types.h>
 
 
 #define MIN_TTYB_SIZE	256
@@ -567,7 +569,15 @@ bool tty_buffer_queue_work(struct tty_port *port)
 
 void tty_buffer_init_kthread(void)
 {
-	kthread_run(kthread_worker_fn, &tty_buffer_worker, "tty");
+	struct sched_param param = { .sched_priority = 1 };
+	struct task_struct *kworker_task;
+
+	kworker_task = kthread_run(kthread_worker_fn, &tty_buffer_worker, "tty");
+	if (IS_ERR(kworker_task)) {
+		pr_err("failed to create message pump task\n");
+		return;
+	}
+	sched_setscheduler(kworker_task, SCHED_FIFO, &param);
 }
 
 /**
-- 
2.19.1

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