[PATCH V3 7/7] blk-mq: don't allocate driver tag beforehand for flush rq
From: Ming Lei
Date: Thu Nov 02 2017 - 11:26:14 EST
The behind idea is simple:
1) for none scheduler, driver tag has to be borrowed for flush rq, otherwise
we may run out of tag, and IO hang is caused. And get/put driver tag is
actually noop, so reorder tags isn't necessary at all.
2) for real I/O scheduler, we needn't to allocate driver tag beforehand for
flush rq, and it works just fine to follow the way for normal requests: allocate
driver tag for each rq just before calling .queue_rq().
One visible change to driver 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 needn't to be treated specially wrt. get/put driver tag, code gets
cleanup much, such as, reorder_tags_to_front() is removed, and we needn't to worry
about request order 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@xxxxxxxxxx>
---
block/blk-flush.c | 35 ++++++++++++++++++++++++++---------
block/blk-mq-sched.c | 42 +++++-------------------------------------
block/blk-mq.c | 41 ++++++-----------------------------------
3 files changed, 37 insertions(+), 81 deletions(-)
diff --git a/block/blk-flush.c b/block/blk-flush.c
index a9773d2075ac..f17170675917 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -231,8 +231,13 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
/* release the tag's ownership to the req cloned from */
spin_lock_irqsave(&fq->mq_flush_lock, flags);
hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu);
- blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
- flush_rq->tag = -1;
+ if (!q->elevator) {
+ blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
+ flush_rq->tag = -1;
+ } else {
+ blk_mq_put_driver_tag_hctx(hctx, flush_rq);
+ flush_rq->internal_tag = -1;
+ }
}
running = &fq->flush_queue[fq->flush_running_idx];
@@ -318,19 +323,26 @@ static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
blk_rq_init(q, flush_rq);
/*
- * Borrow tag from the first request since they can't
- * be in flight at the same time. And acquire the tag's
- * ownership for flush req.
+ * In case of none scheduler, borrow tag from the first request
+ * since they can't be in flight at the same time. And acquire
+ * the tag's ownership for flush req.
+ *
+ * In case of IO scheduler, flush rq need to borrow scheduler tag
+ * just for cheating put/get driver tag.
*/
if (q->mq_ops) {
struct blk_mq_hw_ctx *hctx;
flush_rq->mq_ctx = first_rq->mq_ctx;
- flush_rq->tag = first_rq->tag;
- fq->orig_rq = first_rq;
- hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
- blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
+ if (!q->elevator) {
+ fq->orig_rq = first_rq;
+ flush_rq->tag = first_rq->tag;
+ hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
+ blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
+ } else {
+ flush_rq->internal_tag = first_rq->internal_tag;
+ }
}
flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
@@ -394,6 +406,11 @@ static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
hctx = blk_mq_map_queue(q, ctx->cpu);
+ if (q->elevator) {
+ WARN_ON(rq->tag < 0);
+ blk_mq_put_driver_tag_hctx(hctx, rq);
+ }
+
/*
* After populating an empty queue, kick it to avoid stall. Read
* the comment in flush_end_io().
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 32e4ea2d0a77..eb082f82b470 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -366,29 +366,12 @@ static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
return true;
}
- if (has_sched) {
+ if (has_sched)
rq->rq_flags |= RQF_SORTED;
- WARN_ON(rq->tag != -1);
- }
return false;
}
-/*
- * Add flush/fua to the queue. If we fail getting a driver tag, then
- * punt to the requeue list. Requeue will re-invoke us from a context
- * that's safe to block from.
- */
-static void blk_mq_sched_insert_flush(struct blk_mq_hw_ctx *hctx,
- struct request *rq, bool can_block)
-{
- if (blk_mq_get_driver_tag(rq, &hctx, can_block)) {
- blk_insert_flush(rq);
- blk_mq_run_hw_queue(hctx, true);
- } else
- blk_mq_add_to_requeue_list(rq, false, true);
-}
-
void blk_mq_sched_insert_request(struct request *rq, bool at_head,
bool run_queue, bool async, bool can_block)
{
@@ -399,10 +382,12 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head,
/* flush rq in flush machinery need to be dispatched directly */
if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
- blk_mq_sched_insert_flush(hctx, rq, can_block);
- return;
+ blk_insert_flush(rq);
+ goto run;
}
+ WARN_ON(e && (rq->tag != -1));
+
if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
goto run;
@@ -429,23 +414,6 @@ void blk_mq_sched_insert_requests(struct request_queue *q,
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
struct elevator_queue *e = hctx->queue->elevator;
- if (e) {
- struct request *rq, *next;
-
- /*
- * We bypass requests that already have a driver tag assigned,
- * which should only be flushes. Flushes are only ever inserted
- * as single requests, so we shouldn't ever hit the
- * WARN_ON_ONCE() below (but let's handle it just in case).
- */
- list_for_each_entry_safe(rq, next, list, queuelist) {
- if (WARN_ON_ONCE(rq->tag != -1)) {
- list_del_init(&rq->queuelist);
- blk_mq_sched_bypass_insert(hctx, true, rq);
- }
- }
- }
-
if (e && e->type->ops.mq.insert_requests)
e->type->ops.mq.insert_requests(hctx, list, false);
else
diff --git a/block/blk-mq.c b/block/blk-mq.c
index bf62065a15ec..445c74e0f5e5 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -650,6 +650,8 @@ 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);
@@ -993,30 +995,6 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
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)
{
@@ -1077,9 +1055,6 @@ 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.
@@ -1135,7 +1110,6 @@ 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;
@@ -1704,13 +1678,10 @@ 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;
--
2.9.5