Re: [PATCH v16 00/26] Improve write performance for zoned UFS devices

Bart Van Assche
2024-11-21T18:00:24Z

On 11/20/24 7:20 PM, Damien Le Moal wrote:
> I am only trying to see if there is not a simpler approach than what you did.
> The less changes, the better, right ?

Hi Damien,

I agree with you that we should select the simplest approach that yields
the desired performance.

Regarding the proposed approach, forcing unplugging a zone write plug
from the driver once a command is passed to the driver and the driver
did not reject it, is this approach compatible with SCSI devices that
may report a unit attention? If two zoned writes for the same zone are
submitted in order to a SCSI device and the SCSI device responds with a
unit attention condition to the first write then the second write will
fail with an "unaligned write" error. This will have to be handled by
pausing zoned write submission and by resubmitting zoned writes after
all pending zoned writes for the given zone have completed. In other
words, if higher queue depths are supported per zone, we cannot avoid
increasing the complexity of the code in block/blk-zoned.c. If we cannot
avoid increasing the complexity of that code, I think we can as well
select the approach that yields the highest performance and the fewest
changes in the block layer code for regular reads and writes.

Thanks,

Bart.