Commit 396eaf21 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe

blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback

blk_insert_cloned_request() is called in the fast path of a dm-rq driver
(e.g. blk-mq request-based DM mpath).  blk_insert_cloned_request() uses
blk_mq_request_bypass_insert() to directly append the request to the
blk-mq hctx->dispatch_list of the underlying queue.

1) This way isn't efficient enough because the hctx spinlock is always
used.

2) With blk_insert_cloned_request(), we completely bypass underlying
queue's elevator and depend on the upper-level dm-rq driver's elevator
to schedule IO.  But dm-rq currently can't get the underlying queue's
dispatch feedback at all.  Without knowing whether a request was issued
or not (e.g. due to underlying queue being busy) the dm-rq elevator will
not be able to provide effective IO merging (as a side-effect of dm-rq
currently blindly destaging a request from its elevator only to requeue
it after a delay, which kills any opportunity for merging).  This
obviously causes very bad sequential IO performance.

Fix this by updating blk_insert_cloned_request() to use
blk_mq_request_direct_issue().  blk_mq_request_direct_issue() allows a
request to be issued directly to the underlying queue and returns the
dispatch feedback (blk_status_t).  If blk_mq_request_direct_issue()
returns BLK_SYS_RESOURCE the dm-rq driver will now use DM_MAPIO_REQUEUE
to _not_ destage the request.  Whereby preserving the opportunity to
merge IO.

With this, request-based DM's blk-mq sequential IO performance is vastly
improved (as much as 3X in mpath/virtio-scsi testing).
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
[blk-mq.c changes heavily influenced by Ming Lei's initial solution, but
they were refactored to make them less fragile and easier to read/review]
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 0f95549c
...@@ -2500,8 +2500,7 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request * ...@@ -2500,8 +2500,7 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *
* bypass a potential scheduler on the bottom device for * bypass a potential scheduler on the bottom device for
* insert. * insert.
*/ */
blk_mq_request_bypass_insert(rq, true); return blk_mq_request_direct_issue(rq);
return BLK_STS_OK;
} }
spin_lock_irqsave(q->queue_lock, flags); spin_lock_irqsave(q->queue_lock, flags);
......
...@@ -1775,15 +1775,19 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx, ...@@ -1775,15 +1775,19 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
static void __blk_mq_fallback_to_insert(struct blk_mq_hw_ctx *hctx, static void __blk_mq_fallback_to_insert(struct blk_mq_hw_ctx *hctx,
struct request *rq, struct request *rq,
bool run_queue) bool run_queue, bool bypass_insert)
{ {
blk_mq_sched_insert_request(rq, false, run_queue, false, if (!bypass_insert)
hctx->flags & BLK_MQ_F_BLOCKING); blk_mq_sched_insert_request(rq, false, run_queue, false,
hctx->flags & BLK_MQ_F_BLOCKING);
else
blk_mq_request_bypass_insert(rq, run_queue);
} }
static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
struct request *rq, struct request *rq,
blk_qc_t *cookie) blk_qc_t *cookie,
bool bypass_insert)
{ {
struct request_queue *q = rq->q; struct request_queue *q = rq->q;
bool run_queue = true; bool run_queue = true;
...@@ -1794,7 +1798,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, ...@@ -1794,7 +1798,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
goto insert; goto insert;
} }
if (q->elevator) if (q->elevator && !bypass_insert)
goto insert; goto insert;
if (!blk_mq_get_driver_tag(rq, NULL, false)) if (!blk_mq_get_driver_tag(rq, NULL, false))
...@@ -1807,7 +1811,9 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, ...@@ -1807,7 +1811,9 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
return __blk_mq_issue_directly(hctx, rq, cookie); return __blk_mq_issue_directly(hctx, rq, cookie);
insert: insert:
__blk_mq_fallback_to_insert(hctx, rq, run_queue); __blk_mq_fallback_to_insert(hctx, rq, run_queue, bypass_insert);
if (bypass_insert)
return BLK_STS_RESOURCE;
return BLK_STS_OK; return BLK_STS_OK;
} }
...@@ -1822,15 +1828,30 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, ...@@ -1822,15 +1828,30 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
hctx_lock(hctx, &srcu_idx); hctx_lock(hctx, &srcu_idx);
ret = __blk_mq_try_issue_directly(hctx, rq, cookie); ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false);
if (ret == BLK_STS_RESOURCE) if (ret == BLK_STS_RESOURCE)
__blk_mq_fallback_to_insert(hctx, rq, true); __blk_mq_fallback_to_insert(hctx, rq, true, false);
else if (ret != BLK_STS_OK) else if (ret != BLK_STS_OK)
blk_mq_end_request(rq, ret); blk_mq_end_request(rq, ret);
hctx_unlock(hctx, srcu_idx); hctx_unlock(hctx, srcu_idx);
} }
blk_status_t blk_mq_request_direct_issue(struct request *rq)
{
blk_status_t ret;
int srcu_idx;
blk_qc_t unused_cookie;
struct blk_mq_ctx *ctx = rq->mq_ctx;
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(rq->q, ctx->cpu);
hctx_lock(hctx, &srcu_idx);
ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true);
hctx_unlock(hctx, srcu_idx);
return ret;
}
static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio) static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
{ {
const int is_sync = op_is_sync(bio->bi_opf); const int is_sync = op_is_sync(bio->bi_opf);
......
...@@ -74,6 +74,9 @@ void blk_mq_request_bypass_insert(struct request *rq, bool run_queue); ...@@ -74,6 +74,9 @@ void blk_mq_request_bypass_insert(struct request *rq, bool run_queue);
void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx, void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
struct list_head *list); struct list_head *list);
/* Used by blk_insert_cloned_request() to issue request directly */
blk_status_t blk_mq_request_direct_issue(struct request *rq);
/* /*
* CPU -> queue mappings * CPU -> queue mappings
*/ */
......
...@@ -395,7 +395,7 @@ static void end_clone_request(struct request *clone, blk_status_t error) ...@@ -395,7 +395,7 @@ static void end_clone_request(struct request *clone, blk_status_t error)
dm_complete_request(tio->orig, error); dm_complete_request(tio->orig, error);
} }
static void dm_dispatch_clone_request(struct request *clone, struct request *rq) static blk_status_t dm_dispatch_clone_request(struct request *clone, struct request *rq)
{ {
blk_status_t r; blk_status_t r;
...@@ -404,9 +404,10 @@ static void dm_dispatch_clone_request(struct request *clone, struct request *rq) ...@@ -404,9 +404,10 @@ static void dm_dispatch_clone_request(struct request *clone, struct request *rq)
clone->start_time = jiffies; clone->start_time = jiffies;
r = blk_insert_cloned_request(clone->q, clone); r = blk_insert_cloned_request(clone->q, clone);
if (r) if (r != BLK_STS_OK && r != BLK_STS_RESOURCE)
/* must complete clone in terms of original request */ /* must complete clone in terms of original request */
dm_complete_request(rq, r); dm_complete_request(rq, r);
return r;
} }
static int dm_rq_bio_constructor(struct bio *bio, struct bio *bio_orig, static int dm_rq_bio_constructor(struct bio *bio, struct bio *bio_orig,
...@@ -476,8 +477,10 @@ static int map_request(struct dm_rq_target_io *tio) ...@@ -476,8 +477,10 @@ static int map_request(struct dm_rq_target_io *tio)
struct mapped_device *md = tio->md; struct mapped_device *md = tio->md;
struct request *rq = tio->orig; struct request *rq = tio->orig;
struct request *clone = NULL; struct request *clone = NULL;
blk_status_t ret;
r = ti->type->clone_and_map_rq(ti, rq, &tio->info, &clone); r = ti->type->clone_and_map_rq(ti, rq, &tio->info, &clone);
check_again:
switch (r) { switch (r) {
case DM_MAPIO_SUBMITTED: case DM_MAPIO_SUBMITTED:
/* The target has taken the I/O to submit by itself later */ /* The target has taken the I/O to submit by itself later */
...@@ -492,7 +495,17 @@ static int map_request(struct dm_rq_target_io *tio) ...@@ -492,7 +495,17 @@ static int map_request(struct dm_rq_target_io *tio)
/* The target has remapped the I/O so dispatch it */ /* The target has remapped the I/O so dispatch it */
trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)), trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)),
blk_rq_pos(rq)); blk_rq_pos(rq));
dm_dispatch_clone_request(clone, rq); ret = dm_dispatch_clone_request(clone, rq);
if (ret == BLK_STS_RESOURCE) {
blk_rq_unprep_clone(clone);
tio->ti->type->release_clone_rq(clone);
tio->clone = NULL;
if (!rq->q->mq_ops)
r = DM_MAPIO_DELAY_REQUEUE;
else
r = DM_MAPIO_REQUEUE;
goto check_again;
}
break; break;
case DM_MAPIO_REQUEUE: case DM_MAPIO_REQUEUE:
/* The target wants to requeue the I/O */ /* The target wants to requeue the I/O */
......
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