提交 de148297 编写于 作者: M Ming Lei 提交者: Jens Axboe

blk-mq: introduce .get_budget and .put_budget in blk_mq_ops

For SCSI devices, there is often a per-request-queue depth, which needs
to be respected before queuing one request.

Currently blk-mq always dequeues the request first, then calls
.queue_rq() to dispatch the request to lld. One obvious issue with this
approach is that I/O merging may not be successful, because when the
per-request-queue depth can't be respected, .queue_rq() has to return
BLK_STS_RESOURCE, and then this request has to stay in hctx->dispatch
list. This means it never gets a chance to be merged with other IO.

This patch introduces .get_budget and .put_budget callback in blk_mq_ops,
then we can try to get reserved budget first before dequeuing request.
If the budget for queueing I/O can't be satisfied, we don't need to
dequeue request at all. Hence the request can be left in the IO
scheduler queue, for more merging opportunities.
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
上级 63ba8e31
......@@ -89,31 +89,57 @@ static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
return false;
}
static void blk_mq_do_dispatch_sched(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)
{
struct request_queue *q = hctx->queue;
struct elevator_queue *e = q->elevator;
LIST_HEAD(rq_list);
do {
struct request *rq = e->type->ops.mq.dispatch_request(hctx);
struct request *rq;
blk_status_t ret;
if (!rq)
if (e->type->ops.mq.has_work &&
!e->type->ops.mq.has_work(hctx))
break;
ret = blk_mq_get_dispatch_budget(hctx);
if (ret == BLK_STS_RESOURCE)
return true;
rq = e->type->ops.mq.dispatch_request(hctx);
if (!rq) {
blk_mq_put_dispatch_budget(hctx);
break;
} else if (ret != BLK_STS_OK) {
blk_mq_end_request(rq, ret);
continue;
}
/*
* Now this rq owns the budget which has to be released
* if this rq won't be queued to driver via .queue_rq()
* in blk_mq_dispatch_rq_list().
*/
list_add(&rq->queuelist, &rq_list);
} while (blk_mq_dispatch_rq_list(q, &rq_list));
} while (blk_mq_dispatch_rq_list(q, &rq_list, true));
return false;
}
void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
/* return true if hw queue need to be run again */
bool 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;
return false;
hctx->run++;
......@@ -143,14 +169,23 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
*/
if (!list_empty(&rq_list)) {
blk_mq_sched_mark_restart_hctx(hctx);
if (blk_mq_dispatch_rq_list(q, &rq_list) && has_sched_dispatch)
blk_mq_do_dispatch_sched(hctx);
if (blk_mq_dispatch_rq_list(q, &rq_list, false) &&
has_sched_dispatch)
run_queue = blk_mq_do_dispatch_sched(hctx);
} else if (has_sched_dispatch) {
blk_mq_do_dispatch_sched(hctx);
run_queue = blk_mq_do_dispatch_sched(hctx);
} else {
blk_mq_flush_busy_ctxs(hctx, &rq_list);
blk_mq_dispatch_rq_list(q, &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,
......
......@@ -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);
void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);
bool 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);
......
......@@ -1048,7 +1048,8 @@ static bool blk_mq_dispatch_wait_add(struct blk_mq_hw_ctx *hctx)
return true;
}
bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
bool got_budget)
{
struct blk_mq_hw_ctx *hctx;
struct request *rq;
......@@ -1057,6 +1058,8 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
if (list_empty(list))
return false;
WARN_ON(!list_is_singular(list) && got_budget);
/*
* Now process all the entries, sending them to the driver.
*/
......@@ -1074,16 +1077,30 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
* The initial allocation attempt failed, so we need to
* rerun the hardware queue when a tag is freed.
*/
if (!blk_mq_dispatch_wait_add(hctx))
if (!blk_mq_dispatch_wait_add(hctx)) {
if (got_budget)
blk_mq_put_dispatch_budget(hctx);
break;
}
/*
* It's possible that a tag was freed in the window
* between the allocation failure and adding the
* hardware queue to the wait queue.
*/
if (!blk_mq_get_driver_tag(rq, &hctx, false))
if (!blk_mq_get_driver_tag(rq, &hctx, false)) {
if (got_budget)
blk_mq_put_dispatch_budget(hctx);
break;
}
}
if (!got_budget) {
ret = blk_mq_get_dispatch_budget(hctx);
if (ret == BLK_STS_RESOURCE)
break;
if (ret != BLK_STS_OK)
goto fail_rq;
}
list_del_init(&rq->queuelist);
......@@ -1111,6 +1128,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
break;
}
fail_rq:
if (unlikely(ret != BLK_STS_OK)) {
errors++;
blk_mq_end_request(rq, BLK_STS_IOERR);
......@@ -1169,6 +1187,7 @@ 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
......@@ -1185,15 +1204,18 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
rcu_read_lock();
blk_mq_sched_dispatch_requests(hctx);
run_queue = blk_mq_sched_dispatch_requests(hctx);
rcu_read_unlock();
} else {
might_sleep();
srcu_idx = srcu_read_lock(hctx->queue_rq_srcu);
blk_mq_sched_dispatch_requests(hctx);
run_queue = 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);
}
/*
......@@ -1582,6 +1604,13 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
if (!blk_mq_get_driver_tag(rq, NULL, false))
goto insert;
ret = blk_mq_get_dispatch_budget(hctx);
if (ret == BLK_STS_RESOURCE) {
blk_mq_put_driver_tag(rq);
goto insert;
} else if (ret != BLK_STS_OK)
goto fail_rq;
new_cookie = request_to_qc_t(hctx, rq);
/*
......@@ -1598,6 +1627,7 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
__blk_mq_requeue_request(rq);
goto insert;
default:
fail_rq:
*cookie = BLK_QC_T_NONE;
blk_mq_end_request(rq, ret);
return;
......@@ -2582,6 +2612,9 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
if (!set->ops->queue_rq)
return -EINVAL;
if (!set->ops->get_budget ^ !set->ops->put_budget)
return -EINVAL;
if (set->queue_depth > BLK_MQ_MAX_DEPTH) {
pr_info("blk-mq: reduced tag depth to %u\n",
BLK_MQ_MAX_DEPTH);
......
......@@ -30,7 +30,7 @@ void blk_mq_freeze_queue(struct request_queue *q);
void blk_mq_free_queue(struct request_queue *q);
int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
void blk_mq_wake_waiters(struct request_queue *q);
bool blk_mq_dispatch_rq_list(struct request_queue *, struct list_head *);
bool blk_mq_dispatch_rq_list(struct request_queue *, struct list_head *, bool);
void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list);
bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx);
bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
......@@ -137,4 +137,22 @@ static inline bool blk_mq_hw_queue_mapped(struct blk_mq_hw_ctx *hctx)
void blk_mq_in_flight(struct request_queue *q, struct hd_struct *part,
unsigned int inflight[2]);
static inline void blk_mq_put_dispatch_budget(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
if (q->mq_ops->put_budget)
q->mq_ops->put_budget(hctx);
}
static inline blk_status_t blk_mq_get_dispatch_budget(
struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
if (q->mq_ops->get_budget)
return q->mq_ops->get_budget(hctx);
return BLK_STS_OK;
}
#endif
......@@ -90,6 +90,8 @@ struct blk_mq_queue_data {
typedef blk_status_t (queue_rq_fn)(struct blk_mq_hw_ctx *,
const struct blk_mq_queue_data *);
typedef blk_status_t (get_budget_fn)(struct blk_mq_hw_ctx *);
typedef void (put_budget_fn)(struct blk_mq_hw_ctx *);
typedef enum blk_eh_timer_return (timeout_fn)(struct request *, bool);
typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int);
typedef void (exit_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int);
......@@ -111,6 +113,15 @@ struct blk_mq_ops {
*/
queue_rq_fn *queue_rq;
/*
* Reserve budget before queue request, once .queue_rq is
* run, it is driver's responsibility to release the
* reserved budget. Also we have to handle failure case
* of .get_budget for avoiding I/O deadlock.
*/
get_budget_fn *get_budget;
put_budget_fn *put_budget;
/*
* Called on request timeout
*/
......
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