Re: [PATCH v8 1/5] block: Add independent access ranges support

[Hannes Reinecke <hare@suse.de>]

On 9/9/21 4:35 AM, Damien Le Moal wrote:
> The Concurrent Positioning Ranges VPD page (for SCSI) and data log page
> (for ATA) contain parameters describing the set of contiguous LBAs that
> can be served independently by a single LUN multi-actuator hard-disk.
> Similarly, a logically defined block device composed of multiple disks
> can in some cases execute requests directed at different sector ranges
> in parallel. A dm-linear device aggregating 2 block devices together is
> an example.
> 
> This patch implements support for exposing a block device independent
> access ranges to the user through sysfs to allow optimizing device
> accesses to increase performance.
> 
> To describe the set of independent sector ranges of a device (actuators
> of a multi-actuator HDDs or table entries of a dm-linear device),
> The type struct blk_independent_access_ranges is introduced. This
> structure describes the sector ranges using an array of
> struct blk_independent_access_range structures. This range structure
> defines the start sector and number of sectors of the access range.
> The ranges in the array cannot overlap and must contain all sectors
> within the device capacity.
> 
> The function disk_set_independent_access_ranges() allows a device
> driver to signal to the block layer that a device has multiple
> independent access ranges.  In this case, a struct
> blk_independent_access_ranges is attached to the device request queue
> by the function disk_set_independent_access_ranges(). The function
> disk_alloc_independent_access_ranges() is provided for drivers to
> allocate this structure.
> 
> struct blk_independent_access_ranges contains kobjects (struct kobject)
> to expose to the user through sysfs the set of independent access ranges
> supported by a device. When the device is initialized, sysfs
> registration of the ranges information is done from blk_register_queue()
> using the block layer internal function
> disk_register_independent_access_ranges(). If a driver calls
> disk_set_independent_access_ranges() for a registered queue, e.g. when a
> device is revalidated, disk_set_independent_access_ranges() will execute
> disk_register_independent_access_ranges() to update the sysfs attribute
> files.  The sysfs file structure created starts from the
> independent_access_ranges sub-directory and contains the start sector
> and number of sectors of each range, with the information for each range
> grouped in numbered sub-directories.
> 
> E.g. for a dual actuator HDD, the user sees:
> 
> $ tree /sys/block/sdk/queue/independent_access_ranges/
> /sys/block/sdk/queue/independent_access_ranges/
> |-- 0
> |   |-- nr_sectors
> |   `-- sector
> `-- 1
>      |-- nr_sectors
>      `-- sector
> 
> For a regular device with a single access range, the
> independent_access_ranges sysfs directory does not exist.
> 
> Device revalidation may lead to changes to this structure and to the
> attribute values. When manipulated, the queue sysfs_lock and
> sysfs_dir_lock mutexes are held for atomicity, similarly to how the
> blk-mq and elevator sysfs queue sub-directories are protected.
> 
> The code related to the management of independent access ranges is
> added in the new file block/blk-ia-ranges.c.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>   block/Makefile         |   2 +-
>   block/blk-ia-ranges.c  | 348 +++++++++++++++++++++++++++++++++++++++++
>   block/blk-sysfs.c      |  26 ++-
>   block/blk.h            |   4 +
>   include/linux/blkdev.h |  39 +++++
>   5 files changed, 410 insertions(+), 9 deletions(-)
>   create mode 100644 block/blk-ia-ranges.c
> Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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