blk-wbt: allow reset of default latency through sysfs

Allow a write of '-1' to reset the default latency target for
a given device. This removes knowledge of the different default
settings for rotational vs non-rotational from user space.

Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 9f97594e68ce..92df2f7c5af1 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -675,6 +675,18 @@ void wbt_disable(struct rq_wb *rwb)
 }
 EXPORT_SYMBOL_GPL(wbt_disable);
 
+u64 wbt_default_latency_nsec(struct request_queue *q)
+{
+        /*
+         * We default to 2msec for non-rotational storage, and 75msec
+         * for rotational storage.
+         */
+        if (blk_queue_nonrot(q))
+                return 2000000ULL;
+        else
+                return 75000000ULL;
+}
+
 int wbt_init(struct request_queue *q)
 {
         struct rq_wb *rwb;
@@ -711,10 +723,7 @@ int wbt_init(struct request_queue *q)
         q->rq_wb = rwb;
         blk_stat_enable(q);
 
-        if (blk_queue_nonrot(q))
-                rwb->min_lat_nsec = 2000000ULL;
-        else
-                rwb->min_lat_nsec = 75000000ULL;
+        rwb->min_lat_nsec = wbt_default_latency_nsec(q);
 
         wbt_set_queue_depth(rwb, blk_queue_depth(q));
         wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));