scsi_host_block() calls scsi_internal_device_block() for each
scsi_device, and scsi_internal_device_block() calls
blk_mq_quiesce_queue() for each LUN. However synchronize_rcu is
run from blk_mq_quiesce_queue().
This way may become unnecessary slow in case of lots of LUNs.
Use scsi_internal_device_block_nowait() to implement scsi_host_block(),
so it is enough to run synchronize_rcu() once since scsi never
supports blk-mq's BLK_MQ_F_BLOCKING.
Cc: Steffen Maier <maier@xxxxxxxxxxxxx>
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
V2:
- fix commit log as pointed by Steffen
- add comment on BLK_MQ_F_BLOCKING as suggested by Bart
drivers/scsi/scsi_lib.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 47835c4b4ee0..86007a523145 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2841,11 +2841,26 @@ scsi_host_block(struct Scsi_Host *shost)
struct scsi_device *sdev;
int ret = 0;
+ /*
+ * Call scsi_internal_device_block_nowait then we can avoid to
+ * run synchronize_rcu() for each LUN
+ */
shost_for_each_device(sdev, shost) {
- ret = scsi_internal_device_block(sdev);
+ mutex_lock(&sdev->state_mutex);
+ ret = scsi_internal_device_block_nowait(sdev);
+ mutex_unlock(&sdev->state_mutex);
if (ret)
break;
}
+
+ /*
+ * SCSI never enables blk-mq's BLK_MQ_F_BLOCKING, so run
+ * synchronize_rcu() once is enough
+ */
+ WARN_ON_ONCE(shost->tag_set.flags & BLK_MQ_F_BLOCKING);
+
+ if (!ret)
+ synchronize_rcu();
return ret;
}
EXPORT_SYMBOL_GPL(scsi_host_block);
--
2.25.2
