[PATCH] blk-wbt: don't maintain inflight counts if disabled

[Jens Axboe]

A previous commit removed the ability to have per-rq flags. We used
those flags to maintain inflight counts. Since we don't have those
anymore, we have to always maintain inflight counts, even if wbt is
disabled. This is clearly suboptimal.

Add a queue quiesce around changing the wbt latency settings from sysfs
to work around this. With that, we can reliably put the enabled check in
our bio_to_wbt_flags(), since we know the WBT_TRACKED flag will be
consistent for the lifetime of the request.

Fixes: Fixes: c1c80384c8f ("block: remove external dependency on wbt_flags")
Signed-off-by: Jens Axboe <ax...@kernel.dk>

---

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index bb109bb0a055..3772671cf2bc 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -453,9 +453,26 @@ static ssize_t queue_wb_lat_store(struct request_queue *q, 
const char *page,
        else if (val >= 0)
                val *= 1000ULL;
 
-       wbt_set_min_lat(q, val);
+       /*
+        * Ensure that the queue is idled, in case the latency update
+        * ends up either enabling or disabling wbt completely. We can't
+        * have IO inflight if that happens.
+        */
+       if (q->mq_ops) {
+               blk_mq_freeze_queue(q);
+               blk_mq_quiesce_queue(q);
+       } else
+               blk_queue_bypass_start(q);
 
+       wbt_set_min_lat(q, val);
        wbt_update_limits(q);
+
+       if (q->mq_ops) {
+               blk_mq_unquiesce_queue(q);
+               blk_mq_unfreeze_queue(q);
+       } else
+               blk_queue_bypass_end(q);
+
        return count;
 }
 
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index c9358f1981fb..85e4a40a2a0a 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -540,6 +546,9 @@ static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, 
struct bio *bio)
 {
        enum wbt_flags flags = 0;
 
+       if (!rwb_enabled(rwb))
+               return 0;
+
        if (bio_op(bio) == REQ_OP_READ) {
                flags = WBT_READ;
        } else if (wbt_should_throttle(rwb, bio)) {


-- 
Jens Axboe