[dm-devel] [PATCH V6 12/12] dm: support IO polling for bio-based dm device

[Ming Lei]

From: Jeffle Xu <jefflexu at linux.alibaba.com>

IO polling is enabled when all underlying target devices are capable
of IO polling. The sanity check supports the stacked device model, in
which one dm device may be build upon another dm device. In this case,
the mapped device will check if the underlying dm target device
supports IO polling.

Reviewed-by: Hannes Reinecke <hare at suse.de>
Reviewed-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>
Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 drivers/md/dm-table.c         | 24 ++++++++++++++++++++++++
 drivers/md/dm.c               |  2 ++
 include/linux/device-mapper.h |  1 +
 3 files changed, 27 insertions(+)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 95391f78b8d5..a8f3575fb118 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1509,6 +1509,12 @@ struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
 	return &t->targets[(KEYS_PER_NODE * n) + k];
 }
 
+static int device_not_poll_capable(struct dm_target *ti, struct dm_dev *dev,
+				   sector_t start, sector_t len, void *data)
+{
+	return !blk_queue_poll(bdev_get_queue(dev->bdev));
+}
+
 /*
  * type->iterate_devices() should be called when the sanity check needs to
  * iterate and check all underlying data devices. iterate_devices() will
@@ -1559,6 +1565,11 @@ static int count_device(struct dm_target *ti, struct dm_dev *dev,
 	return 0;
 }
 
+int dm_table_supports_poll(struct dm_table *t)
+{
+	return !dm_table_any_dev_attr(t, device_not_poll_capable, NULL);
+}
+
 /*
  * Check whether a table has no data devices attached using each
  * target's iterate_devices method.
@@ -2079,6 +2090,19 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 
 	dm_update_keyslot_manager(q, t);
 	blk_queue_update_readahead(q);
+
+	/*
+	 * Check for request-based device is remained to
+	 * dm_mq_init_request_queue()->blk_mq_init_allocated_queue().
+	 * For bio-based device, only set QUEUE_FLAG_POLL when all underlying
+	 * devices supporting polling.
+	 */
+	if (__table_type_bio_based(t->type)) {
+		if (dm_table_supports_poll(t))
+			blk_queue_flag_set(QUEUE_FLAG_POLL, q);
+		else
+			blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
+	}
 }
 
 unsigned int dm_table_get_num_targets(struct dm_table *t)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 50b693d776d6..1b160e4e6446 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2175,6 +2175,8 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
 		}
 		break;
 	case DM_TYPE_BIO_BASED:
+		/* tell block layer we are capable of bio polling */
+		md->disk->flags |= GENHD_FL_CAP_BIO_POLL;
 	case DM_TYPE_DAX_BIO_BASED:
 		break;
 	case DM_TYPE_NONE:
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 7f4ac87c0b32..31bfd6f70013 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -538,6 +538,7 @@ unsigned int dm_table_get_num_targets(struct dm_table *t);
 fmode_t dm_table_get_mode(struct dm_table *t);
 struct mapped_device *dm_table_get_md(struct dm_table *t);
 const char *dm_table_device_name(struct dm_table *t);
+int dm_table_supports_poll(struct dm_table *t);
 
 /*
  * Trigger an event.
-- 
2.29.2