Re: [PATCH] scsi: core: Cap initial sdev queue depth at shost.can_queue

[John Garry]

On 20/04/2021 01:02, Ming Lei wrote:
> On Tue, Apr 20, 2021 at 12:06:24AM +0800, John Garry wrote:
> > Function sdev_store_queue_depth() enforces that the sdev queue depth cannot
> > exceed shost.can_queue.
> >
> > However, the LLDD may still set cmd_per_lun > can_queue, which leads to an
> > initial sdev queue depth greater than can_queue.
> >
> > Stop this happened by capping initial sdev queue depth at can_queue.
> >
> > Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
> > ---
> > Topic originally discussed at:
> > https://lore.kernel.org/linux-scsi/85dec8eb-8eab-c7d6-b0fb-5622747c5499@xxxxxxxxxxxx/T/#m5663d0cac657d843b93d0c9a2374f98fc04384b9
> >
> > Last idea there was to error/warn in scsi_add_host() for cmd_per_lun >

Hi Ming,

> No, that isn't my suggestion.

Right, it was what I mentioned.

> > can_queue. However, such a shost driver could still configure the sdev
> > queue depth to be sound value at .slave_configure callback, so now thinking
> > the orig patch better.
>
> As I mentioned last time, why can't we fix ->cmd_per_lun in
> scsi_add_host() using .can_queue?

I would rather not change the values which are provided from the driver. 
I would rather take the original values and try to use them in a sane way.

I have not seen other places where driver shost config values are 
modified by the core code.

Thanks,
John