blk-mq: add trace block plug and unplug for multiple queues

For now, we just trace plug for single queue device or drivers
provide .commit_rqs, and have not trace plug for multiple queues
device. But, unplug events will be recorded when call
blk_mq_flush_plug_list(). Then, trace events will be asymmetrical,
just have unplug and without plug.

This patch add trace plug and unplug for multiple queues device in
blk_mq_make_request(). After that, we can accurately trace plug and
unplug for multiple queues.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -2003,11 +2003,13 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 			plug->rq_count--;
 		}
 		blk_add_rq_to_plug(plug, rq);
+		trace_block_plug(q);
 
 		blk_mq_put_ctx(data.ctx);
 
 		if (same_queue_rq) {
 			data.hctx = same_queue_rq->mq_hctx;
+			trace_block_unplug(q, 1, true);
 			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
 					&cookie, false, true);
 		}