[dm-devel] [PATCH v3 02/11] scsi: sd_zbc: Reduce boot device scan and revalidate time

[Hannes Reinecke]

On 10/12/18 4:30 AM, Damien Le Moal wrote:
> Handling checks of ZBC device capacity using the max_lba field of the
> REPORT ZONES command reply for disks with rc_basis == 0 can be done
> using the same report zones command reply used to check the "same"
> field.
> 
> Avoid executing a report zones command solely to check the disk capacity
> by merging sd_zbc_check_capacity() into sd_zbc_check_zone_size() and
> renaming that function to sd_zbc_check_zones(). This removes a costly
> execution of a full report zones command and so reduces device scan
> duration at boot time as well as the duration of disk revalidate calls.
> 
> Furthermore, setting the partial report bit in the REPORT ZONES command
> cdb can significantly reduce this command execution time as the device
> does not have to count and report the total number of zones that could
> be reported assuming a large enough reply buffer. A non-partial zone
> report is necessary only for the first execution of report zones used to
> check the same field value (to ensure that this value applies to all
> zones of the disk). All other calls to sd_zbc_report_zones() can use a
> partial report to reduce execution time.
> 
> Using a 14 TB ZBC disk, these simple changes reduce device scan time at
> boot from about 3.5s down to about 900ms. Disk revalidate times are also
> reduced from about 450ms down to 230ms.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
> Reviewed-by: Christoph Hellwig <hch at lst.de>
> ---
>   drivers/scsi/sd_zbc.c | 94 ++++++++++++++++++-------------------------
>   1 file changed, 40 insertions(+), 54 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare at suse.com>

... and it'll be your fault if there are drives which do not support the 
'partial' bit :)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare at suse.de			               +49 911 74053 688
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