This one is redundant and should be dropped. I ran git-format-patch
twice after a quick rebase to tweak the subject and header.
Sorry for the confusion.
On Tue, Jan 16 2018 at 11:33pm -0500,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> From: Ming Lei <ming.lei@xxxxxxxxxx>
>
> 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: Ming Lei <ming.lei@xxxxxxxxxx>
> [based _heavily_ on Ming Lei's initial solution, but blk-mq.c changes
> were refactored to make them less fragile and easier to read/review]
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> block/blk-core.c | 3 +--
> block/blk-mq.c | 42 +++++++++++++++++++++++++++++++++---------
> block/blk-mq.h | 3 +++
> drivers/md/dm-rq.c | 19 ++++++++++++++++---
> 4 files changed, 53 insertions(+), 14 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 7ba607527487..55f338020254 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -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
> * insert.
> */
> - blk_mq_request_bypass_insert(rq, true);
> - return BLK_STS_OK;
> + return blk_mq_request_direct_issue(rq);
> }
>
> spin_lock_irqsave(q->queue_lock, flags);
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f30e34a22a6c..81ee3f9124dc 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1706,7 +1706,8 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
> blk_qc_t new_cookie;
> blk_status_t ret;
>
> - new_cookie = request_to_qc_t(hctx, rq);
> + if (cookie)
> + new_cookie = request_to_qc_t(hctx, rq);
>
> /*
> * For OK queue, we are done. For error, caller may kill it.
> @@ -1716,13 +1717,15 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
> ret = q->mq_ops->queue_rq(hctx, &bd);
> switch (ret) {
> case BLK_STS_OK:
> - *cookie = new_cookie;
> + if (cookie)
> + *cookie = new_cookie;
> break;
> case BLK_STS_RESOURCE:
> __blk_mq_requeue_request(rq);
> break;
> default:
> - *cookie = BLK_QC_T_NONE;
> + if (cookie)
> + *cookie = BLK_QC_T_NONE;
> break;
> }
>
> @@ -1731,15 +1734,20 @@ 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,
> struct request *rq,
> - bool run_queue)
> + bool run_queue, bool bypass_insert)
> {
> + if (bypass_insert) {
> + blk_mq_request_bypass_insert(rq, run_queue);
> + return;
> + }
> blk_mq_sched_insert_request(rq, false, run_queue, false,
> hctx->flags & BLK_MQ_F_BLOCKING);
> }
>
> static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
> struct request *rq,
> - blk_qc_t *cookie)
> + blk_qc_t *cookie,
> + bool bypass_insert)
> {
> struct request_queue *q = rq->q;
> bool run_queue = true;
> @@ -1750,7 +1758,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
> goto insert;
> }
>
> - if (q->elevator)
> + if (q->elevator && !bypass_insert)
> goto insert;
>
> if (!blk_mq_get_driver_tag(rq, NULL, false))
> @@ -1763,7 +1771,9 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>
> return __blk_mq_issue_directly(hctx, rq, cookie);
> 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;
> }
> @@ -1778,15 +1788,29 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>
> 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)
> - __blk_mq_fallback_to_insert(hctx. rq, true);
> + __blk_mq_fallback_to_insert(hctx. rq, true, false);
> else if (ret != BLK_STS_OK)
> blk_mq_end_request(rq, ret);
>
> hctx_unlock(hctx, srcu_idx);
> }
>
> +blk_status_t blk_mq_request_direct_issue(struct request *rq)
> +{
> + blk_status_t ret;
> + int srcu_idx;
> + 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, NULL, true);
> + hctx_unlock(hctx, srcu_idx);
> +
> + return ret;
> +}
> +
> 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);
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index 8591a54d989b..e3ebc93646ca 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -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,
> 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
> */
> diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
> index c28357f5cb0e..b7d175e94a02 100644
> --- a/drivers/md/dm-rq.c
> +++ b/drivers/md/dm-rq.c
> @@ -395,7 +395,7 @@ static void end_clone_request(struct request *clone, blk_status_t 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;
>
> @@ -404,9 +404,10 @@ static void dm_dispatch_clone_request(struct request *clone, struct request *rq)
>
> clone->start_time = jiffies;
> 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 */
> dm_complete_request(rq, r);
> + return r;
> }
>
> 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)
> struct mapped_device *md = tio->md;
> struct request *rq = tio->orig;
> struct request *clone = NULL;
> + blk_status_t ret;
>
> r = ti->type->clone_and_map_rq(ti, rq, &tio->info, &clone);
> +check_again:
> switch (r) {
> case DM_MAPIO_SUBMITTED:
> /* 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)
> /* The target has remapped the I/O so dispatch it */
> trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)),
> 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;
> case DM_MAPIO_REQUEUE:
> /* The target wants to requeue the I/O */
> --
> 2.15.0
>
> --
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> dm-devel@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/dm-devel
