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 2904100d2485..fcaa06b9c65a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -581,6 +581,8 @@ struct request_queue {
#define QUEUE_FLAG_HCTX_ACTIVE 28 /* at least one blk-mq hctx is active */
#define QUEUE_FLAG_NOWAIT 29 /* device supports NOWAIT */
#define QUEUE_FLAG_SQ_SCHED 30 /* single queue style io dispatch */
+/* Writes for sequential write required zones may be pipelined. */
+#define QUEUE_FLAG_PIPELINE_ZONED_WRITES 31
#define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_SAME_COMP) | \
@@ -624,6 +626,11 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
#define blk_queue_nowait(q) test_bit(QUEUE_FLAG_NOWAIT, &(q)->queue_flags)
#define blk_queue_sq_sched(q) test_bit(QUEUE_FLAG_SQ_SCHED, &(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);
