Re: [PATCH v1 2/4] virtio: increase virtuqueue size for virtio-scsi and virtio-blk

[Stefano Garzarella <sgarzare@redhat.com>]

On Wed, Sep 08, 2021 at 06:20:49PM +0300, Denis Plotnikov wrote:
>
>On 08.09.2021 16:22, Stefano Garzarella wrote:
>>Message bounced, I use new Denis's email address.
>>
>>On Wed, Sep 08, 2021 at 03:17:16PM +0200, Stefano Garzarella wrote:
>>>Hi Denis,
>>>I just found this discussion since we still have the following 
>>>line in hw/core/machine.c:
>>>   { "vhost-blk-device", "seg_max_adjust", "off"}
>>>
>>>IIUC it was a typo, and I think we should fix it since in the 
>>>future we can have `vhost-blk-device`.
>>>
>>>So, I think we have 2 options:
>>>1. remove that line since for now is useless
>>>2. replace with "vhost-scsi"
>>>
>>>I'm not sure which is the best, what do you suggest?
>>>
>>>Thanks,
>>>Stefano
>
>Hi Stefano
>
>I prefer to just remove the line without replacing. This will keep 
>things exactly like it is now.
>
>Replacing with "vhost-scsi" will affect seg_max (limit to 126) on 
>newly created VMs with machine types using "hw_compat_4_2" and older.
>
>Now, because of the typo (error), their seg-max is queue-size 
>dependent. I'm not sure, if replacing the line may cause any problems, 
>for example on migration: source (queue-size 256, seg max 254) -> 
>destination (queue-size 256, seg max 126). But it will definitely 
>introduce two different behaviors for VMs with "hw_compat_4_2" and 
>older. So, I'd choose the lesser of two evils and keep the things like 
>it's now.
>

Yep, make sense. It was the same concern I had.

Do you want to send a patch to remove it with this explanation?

Thanks for the clarification,
Stefano