Re: [PATCH v6 3/7] scsi: core: Retry unaligned zoned writes

["Martin K. Petersen" <martin.petersen@oracle.com>]

Hi Bart!

> If zoned writes (REQ_OP_WRITE) for a sequential write required zone
> have a starting LBA that differs from the write pointer, e.g. because
> zoned writes have been reordered, then the storage device will respond
> with an UNALIGNED WRITE COMMAND error. Send commands that failed with
> an unaligned write error to the SCSI error handler if zone write
> locking is disabled. Let the SCSI error handler sort SCSI commands per
> LBA before resubmitting these.
>
> If zone write locking is disabled, increase the number of retries for
> write commands sent to a sequential zone to the maximum number of
> outstanding commands because in the worst case the number of times
> reordered zoned writes have to be retried is (number of outstanding
> writes per sequential zone) - 1.

I am afraid that I find falling back to rely on the error handler pretty
kludgy. It seems like there would be a more straightforward way ensure
that request ordering is preserved for devices that are known not to
reorder internally.

I probably missed the finer details of what was discussed while I was
away. But why can't we address the specific corner cases that cause the
unexpected reordering at the block layer? Sorting requests in the SCSI
error handler after a reported failure just seems like papering over the
fact that there's a problem elsewhere.

-- 
Martin K. Petersen	Oracle Linux Engineering