Subject: Re: [PATCH v10 vfio 4/7] vfio/pds: Add VFIO live migration support

From: Jason Gunthorpe <[email-masked]>
Date: Mon, 19 Jun 2023 09:46:46 -0300

On Fri, Jun 16, 2023 at 08:06:21AM +0000, Tian, Kevin wrote:

> Ideally the VMM has an estimation how long a VM can be paused based on
> SLA, to-be-migrated state size, available network bandwidth, etc. and that
> hint should be passed to the kernel so any state transition which may violate
> that expectation can fail quickly to break the migration process and put the
> VM back to the running state.
> 
> Jason/Shameer, is there similar concern in mlx/hisilicon drivers? 

It is handled through the vfio_device_feature_mig_data_size mechanism..

> > +	if (cur == VFIO_DEVICE_STATE_RUNNING_P2P && next ==
> > VFIO_DEVICE_STATE_STOP)
> > +		return NULL;
> 
> I'm not sure whether P2P is actually supported here. By definition
> P2P means the device is stopped but still responds to p2p request
> from other devices. If you look at mlx example it uses different
> cmds between RUNNING->RUNNING_P2P and RUNNING_P2P->STOP.
> 
> But in your case seems you simply move what is required in STOP
> into P2P. Probably you can just remove the support of P2P like
> hisilicon does.

We want new devices to get their architecture right, they need to
support P2P. Didn't we talk about this already and Brett was going to
fix it?

Jason