Re: [PATCH RFC v7 05/12] blk-mq: Record nr_active_requests per queue for when using shared sbitmap

Ming Lei
2020-06-11T04:05:24Z

On Thu, Jun 11, 2020 at 01:29:12AM +0800, John Garry wrote:
> The per-hctx nr_active value can no longer be used to fairly assign a share
> of tag depth per request queue for when using a shared sbitmap, as it does
> not consider that the tags are shared tags over all hctx's.
>
> For this case, record the nr_active_requests per request_queue, and make
> the judgment based on that value.
>
> Also introduce a debugfs version of per-hctx blk_mq_debugfs_attr, omitting
> hctx_active_show() (as blk_mq_hw_ctx.nr_active is no longer maintained for
> the case of shared sbitmap) and other entries which we can add which would
> be revised specifically for when using a shared sbitmap.
>
> Co-developed-with: Kashyap Desai <kashyap.desai@broadcom.com>
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
> block/blk-core.c | 2 ++
> block/blk-mq-debugfs.c | 23 ++++++++++++++++++++++-
> block/blk-mq-tag.c | 10 ++++++----
> block/blk-mq.c | 6 +++---
> block/blk-mq.h | 28 +++++++++++++++++++++++++++-
> include/linux/blkdev.h | 2 ++
> 6 files changed, 62 insertions(+), 9 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 03252af8c82c..c622453c1363 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -529,6 +529,8 @@ struct request_queue *__blk_alloc_queue(int node_id)
> q->backing_dev_info->capabilities = BDI_CAP_CGROUP_WRITEBACK;
> q->node = node_id;
>
> + atomic_set(&q->nr_active_requests_shared_sbitmap, 0);
> +
> timer_setup(&q->backing_dev_info->laptop_mode_wb_timer,
> laptop_mode_timer_fn, 0);
> timer_setup(&q->timeout, blk_rq_timed_out_timer, 0);
> diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
> index a400b6698dff..0fa3af41ab65 100644
> --- a/block/blk-mq-debugfs.c
> +++ b/block/blk-mq-debugfs.c
> @@ -796,6 +796,23 @@ static const struct blk_mq_debugfs_attr blk_mq_debugfs_hctx_attrs[] = {
> {},
> };
>
> +static const struct blk_mq_debugfs_attr blk_mq_debugfs_hctx_shared_sbitmap_attrs[] = {
> + {"state", 0400, hctx_state_show},
> + {"flags", 0400, hctx_flags_show},
> + {"dispatch", 0400, .seq_ops = &hctx_dispatch_seq_ops},
> + {"busy", 0400, hctx_busy_show},
> + {"ctx_map", 0400, hctx_ctx_map_show},
> + {"sched_tags", 0400, hctx_sched_tags_show},
> + {"sched_tags_bitmap", 0400, hctx_sched_tags_bitmap_show},
> + {"io_poll", 0600, hctx_io_poll_show, hctx_io_poll_write},
> + {"dispatched", 0600, hctx_dispatched_show, hctx_dispatched_write},
> + {"queued", 0600, hctx_queued_show, hctx_queued_write},
> + {"run", 0600, hctx_run_show, hctx_run_write},
> + {"active", 0400, hctx_active_show},
> + {"dispatch_busy", 0400, hctx_dispatch_busy_show},
> + {}
> +};

You may use macro or whatever to avoid so the duplication.

> +
> static const struct blk_mq_debugfs_attr blk_mq_debugfs_ctx_attrs[] = {
> {"default_rq_list", 0400, .seq_ops = &ctx_default_rq_list_seq_ops},
> {"read_rq_list", 0400, .seq_ops = &ctx_read_rq_list_seq_ops},
> @@ -878,13 +895,17 @@ void blk_mq_debugfs_register_hctx(struct request_queue *q,
> struct blk_mq_hw_ctx *hctx)
> {
> struct blk_mq_ctx *ctx;
> + struct blk_mq_tag_set *set = q->tag_set;
> char name[20];
> int i;
>
> snprintf(name, sizeof(name), "hctx%u", hctx->queue_num);
> hctx->debugfs_dir = debugfs_create_dir(name, q->debugfs_dir);
>
> - debugfs_create_files(hctx->debugfs_dir, hctx, blk_mq_debugfs_hctx_attrs);
> + if (blk_mq_is_sbitmap_shared(set))
> + debugfs_create_files(hctx->debugfs_dir, hctx, blk_mq_debugfs_hctx_shared_sbitmap_attrs);
> + else
> + debugfs_create_files(hctx->debugfs_dir, hctx, blk_mq_debugfs_hctx_attrs);
>
> hctx_for_each_ctx(hctx, ctx, i)
> blk_mq_debugfs_register_ctx(hctx, ctx);
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 92843e3e1a2a..7db16e49f6f6 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -60,9 +60,11 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
> * For shared tag users, we track the number of currently active users
> * and attempt to provide a fair share of the tag depth for each of them.
> */
> -static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
> +static inline bool hctx_may_queue(struct blk_mq_alloc_data *data,
> struct sbitmap_queue *bt)
> {
> + struct blk_mq_hw_ctx *hctx = data->hctx;
> + struct request_queue *q = data->q;
> unsigned int depth, users;
>
> if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED))
> @@ -84,15 +86,15 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
> * Allow at least some tags
> */
> depth = max((bt->sb.depth + users - 1) / users, 4U);
> - return atomic_read(&hctx->nr_active) < depth;
> + return __blk_mq_active_requests(hctx, q) < depth;

There is big change on 'users' too:

users = atomic_read(&hctx->tags->active_queues);

Originally there is single hctx->tags for these HBAs, now there are many
hctx->tags, so 'users' may become much smaller than before.

Maybe '->active_queues' can be moved to tag_set for blk_mq_is_sbitmap_shared().

> }
>
> static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
> struct sbitmap_queue *bt)
> {
> if (!(data->flags & BLK_MQ_REQ_INTERNAL) &&
> - !hctx_may_queue(data->hctx, bt))
> - return BLK_MQ_NO_TAG;
> + !hctx_may_queue(data, bt))
> + return -1;

BLK_MQ_NO_TAG should have been returned.

> if (data->shallow_depth)
> return __sbitmap_queue_get_shallow(bt, data->shallow_depth);
> else
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 77120dd4e4d5..0f7e062a1665 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -283,7 +283,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
> } else {
> if (data->hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) {
> rq_flags = RQF_MQ_INFLIGHT;
> - atomic_inc(&data->hctx->nr_active);
> + __blk_mq_inc_active_requests(data->hctx, data->q);
> }
> rq->tag = tag;
> rq->internal_tag = BLK_MQ_NO_TAG;
> @@ -527,7 +527,7 @@ void blk_mq_free_request(struct request *rq)
>
> ctx->rq_completed[rq_is_sync(rq)]++;
> if (rq->rq_flags & RQF_MQ_INFLIGHT)
> - atomic_dec(&hctx->nr_active);
> + __blk_mq_dec_active_requests(hctx, q);
>
> if (unlikely(laptop_mode && !blk_rq_is_passthrough(rq)))
> laptop_io_completion(q->backing_dev_info);
> @@ -1073,7 +1073,7 @@ bool blk_mq_get_driver_tag(struct request *rq)
> if (rq->tag >= 0) {
> if (shared) {
> rq->rq_flags |= RQF_MQ_INFLIGHT;
> - atomic_inc(&data.hctx->nr_active);
> + __blk_mq_inc_active_requests(rq->mq_hctx, rq->q);
> }
> data.hctx->tags->rqs[rq->tag] = rq;
> }
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index 1a283c707215..9c1e612c2298 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -202,6 +202,32 @@ static inline bool blk_mq_get_dispatch_budget(struct blk_mq_hw_ctx *hctx)
> return true;
> }
>
> +static inline void __blk_mq_inc_active_requests(struct blk_mq_hw_ctx *hctx,
> + struct request_queue *q)
> +{
> + if (blk_mq_is_sbitmap_shared(q->tag_set))
> + atomic_inc(&q->nr_active_requests_shared_sbitmap);
> + else
> + atomic_inc(&hctx->nr_active);
> +}
> +
> +static inline void __blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx,
> + struct request_queue *q)
> +{
> + if (blk_mq_is_sbitmap_shared(q->tag_set))
> + atomic_dec(&q->nr_active_requests_shared_sbitmap);
> + else
> + atomic_dec(&hctx->nr_active);
> +}
> +
> +static inline int __blk_mq_active_requests(struct blk_mq_hw_ctx *hctx,
> + struct request_queue *q)
> +{
> + if (blk_mq_is_sbitmap_shared(q->tag_set))

I'd suggest to add one hctx version of blk_mq_is_sbitmap_shared() since
q->tag_set is seldom used in fast path, and hctx->flags is more
efficient than tag_set->flags.

Thanks,
Ming