When .queue_rq() returns BLK_STS_RESOURCE(BUSY), we can consider that there is congestion in either low level driver or hardware.
This patch uses EWMA to estimate this congestion threshold, then this threshold can be used to detect/avoid congestion. Signed-off-by: Ming Lei <[email protected]> --- block/blk-mq.c | 14 ++++++++++++++ block/blk-mq.h | 9 +++++++++ include/linux/blk-mq.h | 2 ++ 3 files changed, 25 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 6e0fc80aa151..da50c187c508 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -976,6 +976,18 @@ static bool blk_mq_dispatch_wait_add(struct blk_mq_hw_ctx *hctx) return true; } +static void blk_mq_update_req_dispatch_busy(struct blk_mq_hw_ctx *hctx) +{ + struct sbitmap_queue *sbq; + unsigned depth; + + sbq = &hctx->tags->bitmap_tags; + depth = sbitmap_weight(&sbq->sb); + + /* use EWMA to estimate a threshold for detecting congestion */ + ewma_add(hctx->avg_busy_threshold, depth, 8, 0); +} + bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list) { struct blk_mq_hw_ctx *hctx; @@ -1064,6 +1076,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list) spin_lock(&hctx->lock); list_splice_init(list, &hctx->dispatch); + blk_mq_update_req_dispatch_busy(hctx); spin_unlock(&hctx->lock); /* @@ -1468,6 +1481,7 @@ static void blk_mq_direct_dispatch(struct blk_mq_hw_ctx *hctx, { spin_lock(&hctx->lock); list_add(&rq->queuelist, &hctx->dispatch); + blk_mq_update_req_dispatch_busy(hctx); spin_unlock(&hctx->lock); blk_mq_run_hw_queue(hctx, false); diff --git a/block/blk-mq.h b/block/blk-mq.h index 60b01c0309bc..c4516d2a2d2c 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -133,4 +133,13 @@ static inline bool blk_mq_hw_queue_mapped(struct blk_mq_hw_ctx *hctx) return hctx->nr_ctx && hctx->tags; } +/* borrowed from bcache */ +#define ewma_add(ewma, val, weight, factor) \ +({ \ + (ewma) *= (weight) - 1; \ + (ewma) += (val) << factor; \ + (ewma) /= (weight); \ + (ewma) >> factor; \ +}) + #endif diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 14542308d25b..8694fb39cd80 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -22,6 +22,8 @@ struct blk_mq_hw_ctx { unsigned long flags; /* BLK_MQ_F_* flags */ + unsigned long avg_busy_threshold; + void *sched_data; struct request_queue *queue; struct blk_flush_queue *fq; -- 2.9.4
