Re: [PATCH V3 15/25] smartpqi: fix host qdepth limit

[Martin Wilck <mwilck@suse.com>]

On Tue, 2020-12-15 at 20:23 +0000, Don.Brace@microchip.com wrote:
> Please see answers below. Hope this helps.
> 
> -----Original Message-----
> From: Paul Menzel [mailto:pmenzel@molgen.mpg.de] 
> Sent: Monday, December 14, 2020 11:54 AM
> To: Don Brace - C33706 <Don.Brace@microchip.com>; Kevin Barnett -
> C33748 <Kevin.Barnett@microchip.com>; Scott Teel - C33730 <
> Scott.Teel@microchip.com>; Justin Lindley - C33718 <
> Justin.Lindley@microchip.com>; Scott Benesh - C33703 <
> Scott.Benesh@microchip.com>; Gerry Morong - C33720 <
> Gerry.Morong@microchip.com>; Mahesh Rajashekhara - I30583 <
> Mahesh.Rajashekhara@microchip.com>; hch@infradead.org; 
> joseph.szczypek@hpe.com; POSWALD@suse.com; James E. J. Bottomley <
> jejb@linux.ibm.com>; Martin K. Petersen <martin.petersen@oracle.com>
> Cc: linux-scsi@vger.kernel.org; it+linux-scsi@molgen.mpg.de; Donald
> Buczek <buczek@molgen.mpg.de>; Greg KH <gregkh@linuxfoundation.org>
> Subject: Re: [PATCH V3 15/25] smartpqi: fix host qdepth limit
> 
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> 
> Dear Don, dear Mahesh,
> 
> 
> Am 10.12.20 um 21:35 schrieb Don Brace:
> > From: Mahesh Rajashekhara <mahesh.rajashekhara@microchip.com>
> > 
> > * Correct scsi-mid-layer sending more requests than
> >    exposed host Q depth causing firmware ASSERT issue.
> >    * Add host Qdepth counter.
> 
> This supposedly fixes the regression between Linux 5.4 and 5.9, which
> we reported in [1].
> 
>      kernel: smartpqi 0000:89:00.0: controller is offline: status
> code 0x6100c
>      kernel: smartpqi 0000:89:00.0: controller offline
> 
> Thank you for looking into this issue and fixing it. We are going to
> test this.
> 
> For easily finding these things in the git history or the WWW, it
> would be great if these log messages could be included (in the
> future).
> DON> Thanks for your suggestion. Well add them in the next time.
> 
> Also, that means, that the regression is still present in Linux 5.10,
> released yesterday, and this commit does not apply to these versions.
> 
> DON> They have started 5.10-RC7 now. So possibly 5.11 or 5.12
> depending when all of the patches are applied. The patch in question
> is among 28 other patches.
> 
> Mahesh, do you have any idea, what commit caused the regression and
> why the issue started to show up?
> DON> The smartpqi driver sets two scsi_host_template member fields:
> .can_queue and .nr_hw_queues. But we have not yet converted to
> host_tagset. So the queue_depth becomes nr_hw_queues * can_queue,
> which is more than the hw can support. That can be verified by
> looking at scsi_host.h.
>         /*
>          * In scsi-mq mode, the number of hardware queues supported
> by the LLD.
>          *
>          * Note: it is assumed that each hardware queue has a queue
> depth of
>          * can_queue. In other words, the total queue depth per host
>          * is nr_hw_queues * can_queue. However, for when host_tagset
> is set,
>          * the total queue depth is can_queue.
>          */
> 
> So, until we make this change, the queue_depth change prevents the
> above issue from happening.

can_queue and nr_hw_queues have been set like this as long as the
driver existed. Why did Paul observe a regression with 5.9?

And why can't you simply set can_queue to 
(ctrl_info->scsi_ml_can_queue / nr_hw_queues)?

Regards,
Martin