block: add scalable completion tracking of requests

For legacy block, we simply track them in the request queue. For
blk-mq, we track them on a per-sw queue basis, which we can then
sum up through the hardware queues and finally to a per device
state.

The stats are tracked in, roughly, 0.1s interval windows.

Add sysfs files to display the stats.

The feature is off by default, to avoid any extra overhead. In-kernel
users of it can turn it on by setting QUEUE_FLAG_STATS in the queue
flags. We currently don't turn it on if someone just reads any of
the stats files, that is something we could add as well.

Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 562ac46cb790..4d0044d09984 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -250,4 +250,20 @@ static inline unsigned int blk_qc_t_to_tag(blk_qc_t cookie)
 	return cookie & ((1u << BLK_QC_T_SHIFT) - 1);
 }
 
+struct blk_issue_stat {
+	u64 time;
+};
+
+#define BLK_RQ_STAT_BATCH	64
+
+struct blk_rq_stat {
+	s64 mean;
+	u64 min;
+	u64 max;
+	s32 nr_samples;
+	s32 nr_batch;
+	u64 batch;
+	s64 time;
+};
+
 #endif /* __LINUX_BLK_TYPES_H */