Re: [PATCH v8 1/9] block: Introduce more member variables related to zone write locking

[Damien Le Moal <dlemoal@kernel.org>]

On 8/12/23 06:35, Bart Van Assche wrote:
> Many but not all storage controllers require serialization of zoned writes.
> Introduce a new request queue limit member variable
> (driver_preserves_write_order) that allows block drivers to indicate that
> the order of write commands is preserved and hence that serialization of
> writes per zone is not required.
> 
> Make disk_set_zoned() set 'use_zone_write_lock' only if the block device
> has zones and if the block driver does not preserve the order of write
> requests.
> 
> Cc: Damien Le Moal <dlemoal@kernel.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  block/blk-settings.c   |  7 +++++++
>  include/linux/blkdev.h | 10 ++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 0046b447268f..3a7748af1bef 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -56,6 +56,8 @@ void blk_set_default_limits(struct queue_limits *lim)
>  	lim->alignment_offset = 0;
>  	lim->io_opt = 0;
>  	lim->misaligned = 0;
> +	lim->driver_preserves_write_order = false;
> +	lim->use_zone_write_lock = false;
>  	lim->zoned = BLK_ZONED_NONE;
>  	lim->zone_write_granularity = 0;
>  	lim->dma_alignment = 511;
> @@ -685,6 +687,9 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
>  						   b->max_secure_erase_sectors);
>  	t->zone_write_granularity = max(t->zone_write_granularity,
>  					b->zone_write_granularity);
> +	/* Request-based stacking drivers do not reorder requests. */
> +	t->driver_preserves_write_order = b->driver_preserves_write_order;
> +	t->use_zone_write_lock = b->use_zone_write_lock;

I do not think this is correct as the last target of a multi target device will
dictate the result, regardless of the other targets. So this should be something
like:

	t->driver_preserves_write_order = t->driver_preserves_write_order &&
		b->driver_preserves_write_order;
	t->use_zone_write_lock =
		t->use_zone_write_lock || b->use_zone_write_lock;

However, given that driver_preserves_write_order is initialized as false, this
would always be false. Not sure how to handle that...

>  	t->zoned = max(t->zoned, b->zoned);
>  	return ret;
>  }
> @@ -949,6 +954,8 @@ void disk_set_zoned(struct gendisk *disk, enum blk_zoned_model model)
>  	}
>  
>  	q->limits.zoned = model;
> +	q->limits.use_zone_write_lock = model != BLK_ZONED_NONE &&
> +		!q->limits.driver_preserves_write_order;

I think this needs a comment to explain the condition as it takes a while to
understand it.

>  	if (model != BLK_ZONED_NONE) {
>  		/*
>  		 * Set the zone write granularity to the device logical block

You also should set use_zone_write_lock to false in disk_clear_zone_settings().

In patch 9, ufshcd_auto_hibern8_update() changes the value of
driver_preserves_write_order, which will change the value of use_zone_write_lock
only if disk_set_zoned() is called again after ufshcd_auto_hibern8_update(). Is
that the case ? Is the drive revalidated always after
ufshcd_auto_hibern8_update() is executed ?

> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 2f5371b8482c..2c090a28ec78 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -316,6 +316,16 @@ struct queue_limits {
>  	unsigned char		misaligned;
>  	unsigned char		discard_misaligned;
>  	unsigned char		raid_partial_stripes_expensive;
> +	/*
> +	 * Whether or not the block driver preserves the order of write
> +	 * requests. Set by the block driver.
> +	 */
> +	bool			driver_preserves_write_order;
> +	/*
> +	 * Whether or not zone write locking should be used. Set by
> +	 * disk_set_zoned().
> +	 */
> +	bool			use_zone_write_lock;
>  	enum blk_zoned_model	zoned;
>  
>  	/*

-- 
Damien Le Moal
Western Digital Research