Re: [dm-devel] [PATCH RFC 7/7] dm: add support for IO polling

[JeffleXu <jefflexu@linux.alibaba.com>]

On 12/23/20 7:26 PM, Jeffle Xu wrote:
> Enable iopoll when all underlying target devices supports iopoll.
> 
> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
> ---
>  drivers/md/dm-table.c | 28 ++++++++++++++++++++++++++++
>  drivers/md/dm.c       |  1 +
>  2 files changed, 29 insertions(+)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 188f41287f18..b0cd5bf58c3c 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1791,6 +1791,31 @@ static bool dm_table_requires_stable_pages(struct dm_table *t)
>  	return false;
>  }
>  
> +static int device_supports_poll(struct dm_target *ti, struct dm_dev *dev,
> +				sector_t start, sector_t len, void *data)
> +{
> +	struct request_queue *q = bdev_get_queue(dev->bdev);
> +
> +	return q && test_bit(QUEUE_FLAG_POLL, &q->queue_flags);
> +}
> +
> +static bool dm_table_supports_poll(struct dm_table *t)
> +{
> +	struct dm_target *ti;
> +	unsigned int i;
> +
> +	/* Ensure that all targets support iopoll. */
> +	for (i = 0; i < dm_table_get_num_targets(t); i++) {
> +		ti = dm_table_get_target(t, i);
> +
> +		if (!ti->type->iterate_devices ||
> +		    !ti->type->iterate_devices(ti, device_supports_poll, NULL))
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
>  void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  			       struct queue_limits *limits)
>  {
> @@ -1883,6 +1908,9 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  #endif
>  
>  	blk_queue_update_readahead(q);
> +
> +	if (dm_table_supports_poll(t))
> +		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
>  }
>  

This works in arbitrary bio-based DM stacking. Suppose the following
device stack:

    dm0
    dm1
nvme0  nvme1


dm 0 will check if dm1 has QUEUE_FLAG_POLL flag set.


>  unsigned int dm_table_get_num_targets(struct dm_table *t)
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 03c2b867acaa..ffd2c5ead256 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -3049,6 +3049,7 @@ static const struct pr_ops dm_pr_ops = {
>  };
>  
>  static const struct block_device_operations dm_blk_dops = {
> +	.iopoll = blk_bio_poll,
>  	.submit_bio = dm_submit_bio,
>  	.open = dm_blk_open,
>  	.release = dm_blk_close,
> 

-- 
Thanks,
Jeffle