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authorMing Lei <ming.lei@redhat.com>2017-11-02 23:24:38 +0800
committerJens Axboe <axboe@kernel.dk>2017-11-04 12:40:13 -0600
commit923218f6166a84688973acdc39094f3bee1e9ad4 (patch)
tree1013b8c39764532780292633f7e4214c99480aaf /block/blk-mq.c
parent244c65a3ccaa06fd15cc940315606674d3108b2f (diff)
blk-mq: don't allocate driver tag upfront for flush rq
The idea behind it is simple: 1) for none scheduler, driver tag has to be borrowed for flush rq, otherwise we may run out of tag, and that causes an IO hang. And get/put driver tag is actually noop for none, so reordering tags isn't necessary at all. 2) for a real I/O scheduler, we need not allocate a driver tag upfront for flush rq. It works just fine to follow the same approach as normal requests: allocate driver tag for each rq just before calling ->queue_rq(). One driver visible change is that the driver tag isn't shared in the flush request sequence. That won't be a problem, since we always do that in legacy path. Then flush rq need not be treated specially wrt. get/put driver tag. This cleans up the code - for instance, reorder_tags_to_front() can be removed, and we needn't worry about request ordering in dispatch list for avoiding I/O deadlock. Also we have to put the driver tag before requeueing. Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-mq.c')
-rw-r--r--block/blk-mq.c41
1 files changed, 6 insertions, 35 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 14f6886fbec8..c501cbd0de93 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -653,6 +653,8 @@ static void __blk_mq_requeue_request(struct request *rq)
{
struct request_queue *q = rq->q;
+ blk_mq_put_driver_tag(rq);
+
trace_block_rq_requeue(q, rq);
wbt_requeue(q->rq_wb, &rq->issue_stat);
blk_mq_sched_requeue_request(rq);
@@ -996,30 +998,6 @@ done:
return rq->tag != -1;
}
-/*
- * If we fail getting a driver tag because all the driver tags are already
- * assigned and on the dispatch list, BUT the first entry does not have a
- * tag, then we could deadlock. For that case, move entries with assigned
- * driver tags to the front, leaving the set of tagged requests in the
- * same order, and the untagged set in the same order.
- */
-static bool reorder_tags_to_front(struct list_head *list)
-{
- struct request *rq, *tmp, *first = NULL;
-
- list_for_each_entry_safe_reverse(rq, tmp, list, queuelist) {
- if (rq == first)
- break;
- if (rq->tag != -1) {
- list_move(&rq->queuelist, list);
- if (!first)
- first = rq;
- }
- }
-
- return first != NULL;
-}
-
static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
void *key)
{
@@ -1080,9 +1058,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
rq = list_first_entry(list, struct request, queuelist);
if (!blk_mq_get_driver_tag(rq, &hctx, false)) {
- if (!queued && reorder_tags_to_front(list))
- continue;
-
/*
* The initial allocation attempt failed, so we need to
* rerun the hardware queue when a tag is freed.
@@ -1133,7 +1108,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
nxt = list_first_entry(list, struct request, queuelist);
blk_mq_put_driver_tag(nxt);
}
- blk_mq_put_driver_tag_hctx(hctx, rq);
list_add(&rq->queuelist, list);
__blk_mq_requeue_request(rq);
break;
@@ -1698,13 +1672,10 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
if (unlikely(is_flush_fua)) {
blk_mq_put_ctx(data.ctx);
blk_mq_bio_to_request(rq, bio);
- if (q->elevator) {
- blk_mq_sched_insert_request(rq, false, true, true,
- true);
- } else {
- blk_insert_flush(rq);
- blk_mq_run_hw_queue(data.hctx, true);
- }
+
+ /* bypass scheduler for flush rq */
+ blk_insert_flush(rq);
+ blk_mq_run_hw_queue(data.hctx, true);
} else if (plug && q->nr_hw_queues == 1) {
struct request *last = NULL;