Re: [PATCH 0/2] scsi/libata: A potential tagging fix and improvement

Damien Le Moal
2022-03-16T03:25:42Z

On 3/15/22 19:39, John Garry wrote:
> Two loosely related patches are included:
>
> - Fix for scsi_realloc_sdev_budget_map(). I noticed that the budget token
> for scsi commands was way in excess of the device queue depth, so I
> think we need to fix the sbitmap depth. I need to test this more.
>
> - libata change to use scsi command budget token for qc tag for SAS host.
> I marked this as RFC as for SAS hosts I don't see anything which
> guarantees that the budget size is <= 32 always.
> For libsas hosts we resize the device depth to 32 in the slave configure
> callback, but this seems an unreliable approach since not all hosts may
> call this.
> In addition, I am worried that even if we resize the device depth
> properly in the slave config callback, we may still try to alloc qc tag
> prior to this - in lun scan, for example.
> So we need a way to guarantee that the device queue depth is <= 32
> always, which I would be open to suggestions for.
>
> John Garry (2):
> scsi: core: Fix sbitmap depth in scsi_realloc_sdev_budget_map()
> libata: Use scsi cmnd budget token for qc tag for SAS host
>
> drivers/ata/libata-core.c | 5 +++--
> drivers/ata/libata-sata.c | 21 ++++-----------------
> drivers/ata/libata-scsi.c | 2 +-
> drivers/ata/libata.h | 4 ++--
> drivers/scsi/scsi_scan.c | 5 +++++
> include/linux/libata.h | 1 -
> 6 files changed, 15 insertions(+), 23 deletions(-)
>

I tested this and it is working fine for me. This actually solves the QD
not changing problem I had detected with the pm80xx driver.
Now, doing this:

# cat /sys/block/sde/device/queue_depth
32
# echo 16 > /sys/block/sde/device/queue_depth
# cat /sys/block/sde/device/queue_depth
16

is working as expected.

See my comments on patch 2 for getting final ack and tested tags :)

--
Damien Le Moal
Western Digital Research