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

[Denis Plotnikov]

On 09.09.2021 11:28, Stefano Garzarella wrote:
> 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?

Yes, sure.

I'll do it today.

Denis

> Thanks for the clarification,
> Stefano