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Message-ID: <b77e681d-d180-7434-1675-1fcb10ef4abf@opensource.wdc.com>
Date:   Wed, 16 Mar 2022 12:25:26 +0900
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Subject: Re: [PATCH 0/2] scsi/libata: A potential tagging fix and improvement
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To:     John Garry <john.garry@huawei.com>, jejb@linux.ibm.com,
        martin.petersen@oracle.com, bvanassche@acm.org,
        ming.lei@redhat.com, hch@lst.de, hare@suse.de
Cc:     linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-scsi@vger.kernel.org, martin.wilck@suse.com
References: <1647340746-17600-1-git-send-email-john.garry@huawei.com>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <1647340746-17600-1-git-send-email-john.garry@huawei.com>
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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