mmc: move to a SCHED_FIFO thread

Running mmcqd as a prio 120 thread forces it to compete with standard
user processes for IO performance, especially when the system is under
severe CPU load. Move it to a SCHED_FIFO thread to reduce the impact of
load on IO performance.

bug 25392275

Change-Id: I1edfe73baa25e181367c30c1f40fee886e92b60d

drivers/mmc/card/queue.c

@@ -19,6 +19,7 @@
 
 #include <linux/mmc/card.h>
 #include <linux/mmc/host.h>
+#include <linux/sched/rt.h>
 #include "queue.h"
 
 #define MMC_QUEUE_BOUNCESZ	65536
@@ -59,6 +60,11 @@ static int mmc_queue_thread(void *d)
 	struct request_queue *q = mq->queue;
 	struct mmc_card *card = mq->card;
 
+        struct sched_param scheduler_params = {0};
+        scheduler_params.sched_priority = 1;
+
+        sched_setscheduler(current, SCHED_FIFO, &scheduler_params);
+
 	current->flags |= PF_MEMALLOC;
 	if (card->host->wakeup_on_idle)
 		set_wake_up_idle(true);