[dm-devel] [PATCH v4 02/11] scsi: sd_zbc: Reduce boot device scan and revalidate time

[Martin K. Petersen]

Damien,

> 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.

Acked-by: Martin K. Petersen <martin.petersen at oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering