From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Martin K. Petersen" <martin.petersen@oracle.com>
Subject: Re: [PATCH v4 02/11] scsi: sd_zbc: Reduce boot device
	scan and revalidate time
Date: Tue, 16 Oct 2018 00:50:21 -0400
Message-ID: <yq14ldmv6k2.fsf@oracle.com>
References: <20181012100850.23316-1-damien.lemoal@wdc.com>
	<20181012100850.23316-3-damien.lemoal@wdc.com>
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To: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Jens Axboe <axboe@kernel.dk>, "Martin K . Petersen" <martin.petersen@oracle.com>, Mike Snitzer <snitzer@redhat.com>, linux-block@vger.kernel.org, dm-devel@redhat.com, linux-scsi@vger.kernel.org, Christoph Hellwig <hch@lst.de>, Matias Bjorling <matias.bjorling@wdc.com>
List-Id: linux-scsi@vger.kernel.org


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@oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering