[PATCH v2 3/4] block, bfq: add support to record request size information

[Yu Kuai <yukuai3@huawei.com>]

If bfq keep dispatching requests with same size, the following
information are stored if CONFIG_BFQ_GROUP_IOSCHED is enabled:

1) the size
2) the count of requests
3) when the first request was dispatched

These will be used in later patch to support concurrent sync
io in such situation.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/bfq-iosched.c | 15 +++++++++++++++
 block/bfq-iosched.h | 16 ++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index a780205a1be4..7df3fc0ef4ef 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4936,6 +4936,20 @@ static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
 		bfq_tot_busy_queues(bfqd) > 0;
 }
 
+static void bfq_update_dispatch_size_info(struct bfq_data *bfqd,
+					  unsigned int size)
+{
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	if (bfqd->dispatch_size == size) {
+		bfqd->dispatch_count++;
+	} else {
+		bfqd->dispatch_size = size;
+		bfqd->dispatch_count = 1;
+		bfqd->dispatch_time = jiffies;
+	}
+#endif
+}
+
 static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
 {
 	struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
@@ -5019,6 +5033,7 @@ static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
 		bfqd->rq_in_driver++;
 start_rq:
 		rq->rq_flags |= RQF_STARTED;
+		bfq_update_dispatch_size_info(bfqd, blk_rq_bytes(rq));
 	}
 exit:
 	return rq;
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 610769214f72..9ab498839e7c 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -777,6 +777,22 @@ struct bfq_data {
 	 * function)
 	 */
 	unsigned int word_depths[2][2];
+
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	/* the size of last dispatched request */
+	unsigned int dispatch_size;
+	/*
+	 * If bfq keep dispatching requests with same size, this store the
+	 * count of requests. We use unsigned long here, so we don't care
+	 * about overflow.
+	 */
+	unsigned long dispatch_count;
+	/*
+	 * If bfq keep dispatching requests with same size, this store the
+	 * time when the first request was dispatched.
+	 */
+	unsigned long dispatch_time;
+#endif
 };
 
 enum bfqq_state_flags {
-- 
2.31.1