blk-mq: don't restart queue when .get_budget returns BLK_STS_RESOURCE

SCSI restarts its queue in scsi_end_request() automatically, so we don't
need to handle this case in blk-mq.

Especailly any request won't be dequeued in this case, we needn't to
worry about IO hang caused by restart vs. dispatch.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index daab27feb653941afc6677bc215cdf8a58b33bdc..7775f6b12fa94936b3944d899b4aaf147880a5db 100644 (file)
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -81,8 +81,12 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
        }
 }
 
-/* return true if hctx need to run again */
-static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
+/*
+ * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
+ * its queue by itself in its completion handler, so we don't need to
+ * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
+ */
+static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 {
        struct request_queue *q = hctx->queue;
        struct elevator_queue *e = q->elevator;
@@ -98,7 +102,7 @@ static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 
                ret = blk_mq_get_dispatch_budget(hctx);
                if (ret == BLK_STS_RESOURCE)
-                       return true;
+                       break;
 
                rq = e->type->ops.mq.dispatch_request(hctx);
                if (!rq) {
@@ -116,8 +120,6 @@ static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
                 */
                list_add(&rq->queuelist, &rq_list);
        } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
-
-       return false;
 }
 
 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
@@ -131,8 +133,12 @@ static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
        return hctx->ctxs[idx];
 }
 
-/* return true if hctx need to run again */
-static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
+/*
+ * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
+ * its queue by itself in its completion handler, so we don't need to
+ * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
+ */
+static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 {
        struct request_queue *q = hctx->queue;
        LIST_HEAD(rq_list);
@@ -147,7 +153,7 @@ static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 
                ret = blk_mq_get_dispatch_budget(hctx);
                if (ret == BLK_STS_RESOURCE)
-                       return true;
+                       break;
 
                rq = blk_mq_dequeue_from_ctx(hctx, ctx);
                if (!rq) {
@@ -171,22 +177,19 @@ static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
        } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 
        WRITE_ONCE(hctx->dispatch_from, ctx);
-
-       return false;
 }
 
 /* return true if hw queue need to be run again */
-bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
+void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 {
        struct request_queue *q = hctx->queue;
        struct elevator_queue *e = q->elevator;
        const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
        LIST_HEAD(rq_list);
-       bool run_queue = false;
 
        /* RCU or SRCU read lock is needed before checking quiesced flag */
        if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
-               return false;
+               return;
 
        hctx->run++;
 
@@ -218,12 +221,12 @@ bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
                blk_mq_sched_mark_restart_hctx(hctx);
                if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
                        if (has_sched_dispatch)
-                               run_queue = blk_mq_do_dispatch_sched(hctx);
+                               blk_mq_do_dispatch_sched(hctx);
                        else
-                               run_queue = blk_mq_do_dispatch_ctx(hctx);
+                               blk_mq_do_dispatch_ctx(hctx);
                }
        } else if (has_sched_dispatch) {
-               run_queue = blk_mq_do_dispatch_sched(hctx);
+               blk_mq_do_dispatch_sched(hctx);
        } else if (q->mq_ops->get_budget) {
                /*
                 * If we need to get budget before queuing request, we
@@ -233,19 +236,11 @@ bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
                 * TODO: get more budgets, and dequeue more requests in
                 * one time.
                 */
-               run_queue = blk_mq_do_dispatch_ctx(hctx);
+               blk_mq_do_dispatch_ctx(hctx);
        } else {
                blk_mq_flush_busy_ctxs(hctx, &rq_list);
                blk_mq_dispatch_rq_list(q, &rq_list, false);
        }
-
-       if (run_queue && !blk_mq_sched_needs_restart(hctx) &&
-                       !test_bit(BLK_MQ_S_TAG_WAITING, &hctx->state)) {
-               blk_mq_sched_mark_restart_hctx(hctx);
-               return true;
-       }
-
-       return false;
 }
 
 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,

diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index 2434061cc5b75dabf61a4eda7b56483137a840af..9267d0b7c1978ae1a01dc218f07c1e16cb6643cc 100644 (file)
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -22,7 +22,7 @@ void blk_mq_sched_insert_requests(struct request_queue *q,
                                  struct blk_mq_ctx *ctx,
                                  struct list_head *list, bool run_queue_async);
 
-bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);
+void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);
 
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e);
 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 097ca3ece716ee126960b95c2b1824fc60425c1f..e4d2490f4e7eed7fb288f93028c82798291ff0c3 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1226,7 +1226,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 {
        int srcu_idx;
-       bool run_queue;
 
        /*
         * We should be running this queue from one of the CPUs that
@@ -1243,18 +1242,15 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 
        if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
                rcu_read_lock();
-               run_queue = blk_mq_sched_dispatch_requests(hctx);
+               blk_mq_sched_dispatch_requests(hctx);
                rcu_read_unlock();
        } else {
                might_sleep();
 
                srcu_idx = srcu_read_lock(hctx->queue_rq_srcu);
-               run_queue = blk_mq_sched_dispatch_requests(hctx);
+               blk_mq_sched_dispatch_requests(hctx);
                srcu_read_unlock(hctx->queue_rq_srcu, srcu_idx);
        }
-
-       if (run_queue)
-               blk_mq_run_hw_queue(hctx, true);
 }
 
 /*