linux-kernel - Re: [PATCH] scsi: core: Cap initial sdev queue depth at shost.can

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Message-ID: <186be6c5-dbcd-d1fb-67c5-72b5a761568a@huawei.com>
Date:   Thu, 22 Apr 2021 17:35:42 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
        <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kashyap.desai@...adcom.com>, <dgilbert@...erlog.com>
Subject: Re: [PATCH] scsi: core: Cap initial sdev queue depth at
 shost.can_queue

On 22/04/2021 02:38, Ming Lei wrote:
>> 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.

Hi Ming,

> Wrt. .cmd_per_lun, I think it is safe to modify it into one correct
> depth because almost all drivers are just producer of .cmd_per_lun. And
> except for debug purpose, there are only three consumers of .cmd_per_lun
> in scsi, and all are for scsi_change_queue_depth():
> 
> 	process_message()
> 	scsi_alloc_sdev()
> 	virtscsi_change_queue_depth()

sg_ioctl_common() also looks to read it, but I can't imagine we could 
break that interface with either suggested change.

So I still prefer not to modify shost.cmd_per_lun, but if you feel 
strongly enough then I can look to make that change.

Thanks,
John