Writes in sequential write required zones must happen at the write
pointer. Even if the submitter of the write commands (e.g. a filesystem)
submits writes for sequential write required zones in order, the block
layer or the storage controller may reorder these write commands.
The zone locking mechanism in the mq-deadline I/O scheduler serializes
write commands for sequential zones. Some but not all storage controllers
require this serialization. Introduce a new flag such that block drivers
can request pipelining of writes for sequential write required zones.
An example of a storage controller standard that requires write
serialization is AHCI (Advanced Host Controller Interface). Submitting
commands to AHCI controllers happens by writing a bit pattern into a
register. Each set bit corresponds to an active command. This mechanism
does not preserve command ordering information.
Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
include/linux/blkdev.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ef93e848b1fd..b4b4cd3f2912 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -553,6 +553,8 @@ struct request_queue {
#define QUEUE_FLAG_NONROT 6 /* non-rotational device (SSD) */
#define QUEUE_FLAG_VIRT QUEUE_FLAG_NONROT /* paravirt device */
#define QUEUE_FLAG_IO_STAT 7 /* do disk/partitions IO accounting */
+/* Writes for sequential write required zones may be pipelined. */
+#define QUEUE_FLAG_PIPELINE_ZONED_WRITES 8
#define QUEUE_FLAG_NOXMERGES 9 /* No extended merges */
#define QUEUE_FLAG_ADD_RANDOM 10 /* Contributes to random pool */
#define QUEUE_FLAG_SAME_FORCE 12 /* force complete on same CPU */
@@ -614,6 +616,11 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
#define blk_queue_skip_tagset_quiesce(q) \
test_bit(QUEUE_FLAG_SKIP_TAGSET_QUIESCE, &(q)->queue_flags)
+static inline bool blk_queue_pipeline_zoned_writes(struct request_queue *q)
+{
+ return test_bit(QUEUE_FLAG_PIPELINE_ZONED_WRITES, &q->queue_flags);
+}
+
extern void blk_set_pm_only(struct request_queue *q);
extern void blk_clear_pm_only(struct request_queue *q);
