Currently, at the time of completeion, there's no way of knowing how big a
request was. blk-iocost will need this information to account for IO size when
calculating expected latencies.
This patch adds rq->io_data_len which remembers blk_rq_bytes() at the time the
request gets issued. The field is enabled iff CONFIG_BLK_IO_DATA_LEN is set and
doesn't increase the size of the struct even when enabled.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
block/Kconfig | 3 +++
block/blk-mq.c | 6 ++++++
include/linux/blkdev.h | 8 ++++++++
3 files changed, 17 insertions(+)
diff --git a/block/Kconfig b/block/Kconfig
index 3bc76bb113a0..48308e600dc8 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -26,6 +26,9 @@ menuconfig BLOCK
if BLOCK
+config BLK_RQ_IO_DATA_LEN
+ bool
+
config BLK_RQ_ALLOC_TIME
bool
diff --git a/block/blk-mq.c b/block/blk-mq.c
index f6291ceedee4..64ed22712fe4 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -415,6 +415,9 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
return ERR_PTR(-EWOULDBLOCK);
rq->__data_len = 0;
+#ifdef CONFIG_BLK_RQ_IO_DATA_LEN
+ rq->io_data_len = 0;
+#endif
rq->__sector = (sector_t) -1;
rq->bio = rq->biotail = NULL;
return rq;
@@ -655,6 +658,9 @@ void blk_mq_start_request(struct request *rq)
trace_block_rq_issue(q, rq);
+#ifdef CONFIG_BLK_RQ_IO_DATA_LEN
+ rq->io_data_len = blk_rq_bytes(rq);
+#endif
if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
rq->io_start_time_ns = ktime_get_ns();
rq->stats_sectors = blk_rq_sectors(rq);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 32868fbedc9e..bfd34c6a27ef 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -142,6 +142,14 @@ struct request {
/* the following two fields are internal, NEVER access directly */
unsigned int __data_len; /* total data len */
+#ifdef CONFIG_BLK_RQ_IO_DATA_LEN
+ /*
+ * Total data len at the time of issue. This doesn't get deducted by
+ * blk_update_request() and can be used by completion path to determine
+ * the request size.
+ */
+ unsigned int io_data_len;
+#endif
sector_t __sector; /* sector cursor */
struct bio *bio;
--
2.25.1
