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

John Garry
2020-06-11T10:24:12Z

>> +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.

Let me check alternatives.

>
>> +
>> 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.

Can you please check how I handled that in the next patch? There we
record the number of active request queues per set.

(I will note that I could have combined some of these patches, but I
liked the piecemeal appraoch, and none of these paths are enabled until
later).

>
> 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.

OK, I missed that in the rebase.

>
>> 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.

OK

Thanks,
John