Re: [PATCH 2/5] scsi: Retry unaligned zoned writes

From: Bart Van Assche <bvanassche@acm.org>
To: Damien Le Moal <damien.lemoal@opensource.wdc.com>,
	Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	Damien Le Moal <damien.lemoal@wdc.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	Khazhy Kumykov <khazhy@google.com>,
	Jaegeuk Kim <jaegeuk@kernel.org>
Subject: Re: [PATCH 2/5] scsi: Retry unaligned zoned writes
Date: Wed, 15 Jun 2022 12:38:25 -0700	[thread overview]
Message-ID: <6096a273-c88d-3e15-927a-add3071ffbad@acm.org> (raw)
In-Reply-To: <434cb0ae-a6e7-62a0-81dc-cd86f55108d4@opensource.wdc.com>

On 6/15/22 00:21, Damien Le Moal wrote:
> On 6/15/22 14:49, Christoph Hellwig wrote:
>> On Tue, Jun 14, 2022 at 04:56:52PM -0700, Bart Van Assche wrote:
>>> The performance penalty of zone locking is not acceptable for our use case.
>>> Does this mean that zone locking needs to be preserved for AHCI but not for
>>> UFS?
>>
>> It means you use case needs to use zone append, and we need to make sure
>> it is added to SCSI assuming your are on SCSI based on your other comments.
> 
> For scsi, we already have the zone append emulation in the sd driver which
> issues regular writes together with taking the zone lock. So UFS has zone
> append, not as a native command though. But if for UFS device there are no
> issue of command reordering underneath sd, then the zone append emulation
> can be done without taking the zone write lock, which would result in the
> same performance as what a native zone append command would give.
> 
> At least for the short term, that could be a good solution until native
> zone append is added to zbc specs. That last part may face a lot of
> pushback because of the difficulty of having that same command on ATA side.

Is there more information available about the difficulties of defining a 
ZONE APPEND command for ATA? It seems to me that there is enough space 
available in the ATA Status Return Descriptor to report the LBA back to 
the host?

Thanks,

Bart.