The block layer may call the I/O scheduler .finish_request() callback
without having called the .insert_requests() callback. Make sure that the
mq-deadline I/O statistics are correct if the block layer inserts an I/O
request that bypasses the I/O scheduler. This patch prevents that lower
priority I/O is delayed longer than necessary for mixed I/O priority
workloads.
Cc: Niklas Cassel <Niklas.Cassel@xxxxxxx>
Cc: Damien Le Moal <damien.lemoal@xxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Reported-by: Niklas Cassel <Niklas.Cassel@xxxxxxx>
Fixes: 08a9ad8bf607 ("block/mq-deadline: Add cgroup support")
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/mq-deadline.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index dbd74bae9f11..28f2e7655a5f 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -713,6 +713,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
prio = ioprio_class_to_prio[ioprio_class];
dd_count(dd, inserted, prio);
+ rq->elv.priv[0] = (void *)(uintptr_t)1;
if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
blk_mq_free_requests(&free);
@@ -761,12 +762,10 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
spin_unlock(&dd->lock);
}
-/*
- * Nothing to do here. This is defined only to ensure that .finish_request
- * method is called upon request completion.
- */
+/* Callback from inside blk_mq_rq_ctx_init(). */
static void dd_prepare_request(struct request *rq)
{
+ rq->elv.priv[0] = NULL;
}
/*
@@ -793,7 +792,14 @@ static void dd_finish_request(struct request *rq)
const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
struct dd_per_prio *per_prio = &dd->per_prio[prio];
- dd_count(dd, completed, prio);
+ /*
+ * The block layer core may call dd_finish_request() without having
+ * called dd_insert_requests(). Hence only update statistics for
+ * requests for which dd_insert_requests() has been called. See also
+ * blk_mq_request_bypass_insert().
+ */
+ if (rq->elv.priv[0])
+ dd_count(dd, completed, prio);
if (blk_queue_is_zoned(q)) {
unsigned long flags;
