[PATCH 2/2] block/mq-deadline: add module parameter for prio_aging_expire default

[Ye Bin <yebin@huaweicloud.com>]

From: Ye Bin <yebin10@huawei.com>

Allow the default value of prio_aging_expire to be overridden at load
time, in milliseconds to match the sysfs attribute:

  - built-in:  mq_deadline.prio_aging_expire=0 on the kernel command line
  - module:    modprobe mq_deadline prio_aging_expire=0

A value of zero disables I/O priority from boot/load: every request is
filed in the best-effort bucket and the priority aging path is
bypassed, so systems that do not want RT/BE/IDLE distinction can opt
out without writing to sysfs after every queue creation.

Previously prio_aging_expire was a compile-time constant (10 * HZ)
with no way to change the default before the first request queue was
initialized.  Make the variable a module_param so that the override
works whether mq-deadline is built-in or compiled as a module, and
convert the millisecond value to jiffies in dd_init_sched() when
assigning the per-queue default.

Signed-off-by: Ye Bin <yebin10@huawei.com>
---
 block/mq-deadline.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index e3314f7aed8b..95a00a673be5 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -33,7 +33,10 @@ static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SO
  * Time after which to dispatch lower priority requests even if higher
  * priority requests are pending.
  */
-static const int prio_aging_expire = 10 * HZ;
+static int prio_aging_expire = 10 * MSEC_PER_SEC;
+module_param(prio_aging_expire, int, 0644);
+MODULE_PARM_DESC(prio_aging_expire,
+		 "Default prio_aging_expire in milliseconds; 0 disables I/O priority.");
 static const int writes_starved = 2;    /* max times reads can starve a write */
 static const int fifo_batch = 16;       /* # of sequential requests treated as one
 				     by the above parameters. For throughput. */
@@ -559,7 +562,7 @@ static int dd_init_sched(struct request_queue *q, struct elevator_queue *eq)
 	dd->front_merges = 1;
 	dd->last_dir = DD_WRITE;
 	dd->fifo_batch = fifo_batch;
-	dd->prio_aging_expire = prio_aging_expire;
+	dd->prio_aging_expire = msecs_to_jiffies(prio_aging_expire);
 	spin_lock_init(&dd->lock);
 
 	/* We dispatch from request queue wide instead of hw queue */
-- 
2.34.1