diff mbox series

[V5,11/12] block: add poll_capable method to support bio-based IO polling

Message ID 20210401021927.343727-12-ming.lei@redhat.com (mailing list archive)
State New
Headers show
Series block: support bio based io polling | expand

Commit Message

Ming Lei April 1, 2021, 2:19 a.m. UTC
From: Jeffle Xu <jefflexu@linux.alibaba.com>

This method can be used to check if bio-based device supports IO polling
or not. For mq devices, checking for hw queue in polling mode is
adequate, while the sanity check shall be implementation specific for
bio-based devices. For example, dm device needs to check if all
underlying devices are capable of IO polling.

Though bio-based device may have done the sanity check during the
device initialization phase, cacheing the result of this sanity check
(such as by cacheing in the queue_flags) may not work. Because for dm
devices, users could change the state of the underlying devices through
'/sys/block/<dev>/io_poll', bypassing the dm device above. In this case,
the cached result of the very beginning sanity check could be
out-of-date. Thus the sanity check needs to be done every time 'io_poll'
is to be modified.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-sysfs.c      | 14 +++++++++++---
 include/linux/blkdev.h |  1 +
 2 files changed, 12 insertions(+), 3 deletions(-)

Comments

Christoph Hellwig April 12, 2021, 9:38 a.m. UTC | #1
On Thu, Apr 01, 2021 at 10:19:26AM +0800, Ming Lei wrote:
> From: Jeffle Xu <jefflexu@linux.alibaba.com>
> 
> This method can be used to check if bio-based device supports IO polling
> or not. For mq devices, checking for hw queue in polling mode is
> adequate, while the sanity check shall be implementation specific for
> bio-based devices. For example, dm device needs to check if all
> underlying devices are capable of IO polling.
> 
> Though bio-based device may have done the sanity check during the
> device initialization phase, cacheing the result of this sanity check
> (such as by cacheing in the queue_flags) may not work. Because for dm
> devices, users could change the state of the underlying devices through
> '/sys/block/<dev>/io_poll', bypassing the dm device above. In this case,
> the cached result of the very beginning sanity check could be
> out-of-date. Thus the sanity check needs to be done every time 'io_poll'
> is to be modified.

I really don't think thi should be a method, and I really do dislike
how we have all this "if (is_mq)" junk.  Why can't we have a flag on
the gendisk that signals if the device can support polling that
is autoamtically set for blk-mq and as-needed by bio based drivers?
And please move everything that significantly hanges things for the
mq based path to separate prep patches early in th series.

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diff mbox series

Patch

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index db3268d41274..c8e7e4af66cb 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -426,9 +426,17 @@  static ssize_t queue_poll_store(struct request_queue *q, const char *page,
 	unsigned long poll_on;
 	ssize_t ret;
 
-	if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
-	    !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)
-		return -EINVAL;
+	if (queue_is_mq(q)) {
+		if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
+		    !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)
+			return -EINVAL;
+	} else {
+		struct gendisk *disk = queue_to_disk(q);
+
+		if (!disk->fops->poll_capable ||
+		    !disk->fops->poll_capable(disk))
+			return -EINVAL;
+	}
 
 	ret = queue_var_store(&poll_on, page, count);
 	if (ret < 0)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index bfab74b45f15..a46f975f2a2f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1881,6 +1881,7 @@  struct block_device_operations {
 	int (*report_zones)(struct gendisk *, sector_t sector,
 			unsigned int nr_zones, report_zones_cb cb, void *data);
 	char *(*devnode)(struct gendisk *disk, umode_t *mode);
+	bool (*poll_capable)(struct gendisk *disk);
 	struct module *owner;
 	const struct pr_ops *pr_ops;
 };