blk-mq: dequeue request one by one from sw queue if hctx is busy (6e768717) · Commits · 戴 / test

block/blk-mq-debugfs.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -622,6 +622,14 @@ static int hctx_active_show(void data, struct seq_file m)
		return 0;
		}

		static int hctx_dispatch_busy_show(void data, struct seq_file m)
		{
		struct blk_mq_hw_ctx *hctx = data;

		seq_printf(m, "%u\n", hctx->dispatch_busy);
		return 0;
		}

		static void ctx_rq_list_start(struct seq_file m, loff_t *pos)
		__acquires(&ctx->lock)
		{
		@@ -783,6 +791,7 @@ static const struct blk_mq_debugfs_attr blk_mq_debugfs_hctx_attrs[] = {
		{"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},
		{},
		};

+2 −9

Original line number	Diff line number	Diff line
		@@ -206,15 +206,8 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
		}
		} else if (has_sched_dispatch) {
		blk_mq_do_dispatch_sched(hctx);
		} else if (q->mq_ops->get_budget) {
		/*
		* If we need to get budget before queuing request, we
		* dequeue request one by one from sw queue for avoiding
		* to mess up I/O merge when dispatch runs out of resource.
		*
		* TODO: get more budgets, and dequeue more requests in
		* one time.
		*/
		} else if (hctx->dispatch_busy) {
		/* dequeue request one by one from sw queue if queue is busy */
		blk_mq_do_dispatch_ctx(hctx);
		} else {
		blk_mq_flush_busy_ctxs(hctx, &rq_list);

+32 −1

Original line number	Diff line number	Diff line
		@@ -1074,6 +1074,35 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
		return true;
		}

		#define BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT 8
		#define BLK_MQ_DISPATCH_BUSY_EWMA_FACTOR 4
		/*
		* Update dispatch busy with the Exponential Weighted Moving Average(EWMA):
		* - EWMA is one simple way to compute running average value
		* - weight(7/8 and 1/8) is applied so that it can decrease exponentially
		* - take 4 as factor for avoiding to get too small(0) result, and this
		* factor doesn't matter because EWMA decreases exponentially
		*/
		static void blk_mq_update_dispatch_busy(struct blk_mq_hw_ctx *hctx, bool busy)
		{
		unsigned int ewma;

		if (hctx->queue->elevator)
		return;

		ewma = hctx->dispatch_busy;

		if (!ewma && !busy)
		return;

		ewma *= BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT - 1;
		if (busy)
		ewma += 1 << BLK_MQ_DISPATCH_BUSY_EWMA_FACTOR;
		ewma /= BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT;

		hctx->dispatch_busy = ewma;
		}

		#define BLK_MQ_RESOURCE_DELAY 3 /* ms units */

		/*
		@@ -1210,8 +1239,10 @@ bool blk_mq_dispatch_rq_list(struct request_queue q, struct list_head list,
		else if (needs_restart && (ret == BLK_STS_RESOURCE))
		blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);

		blk_mq_update_dispatch_busy(hctx, true);
		return false;
		}
		} else
		blk_mq_update_dispatch_busy(hctx, false);

		/*
		* If the host/device is unable to accept more work, inform the

+2 −1

Original line number	Diff line number	Diff line
		@@ -35,9 +35,10 @@ struct blk_mq_hw_ctx {
		struct sbitmap ctx_map;

		struct blk_mq_ctx *dispatch_from;
		unsigned int dispatch_busy;

		struct blk_mq_ctx **ctxs;
		unsigned int nr_ctx;
		struct blk_mq_ctx **ctxs;

		spinlock_t dispatch_wait_lock;
		wait_queue_entry_t dispatch_wait;