netdev - Re: [PATCH V2 mlx5-next 12/14] vfio/mlx5: Implement vfio

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Date:   Tue, 26 Oct 2021 09:40:34 +0100
From:   "Dr. David Alan Gilbert" <dgilbert@...hat.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>, bhelgaas@...gle.com,
        saeedm@...dia.com, linux-pci@...r.kernel.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, kuba@...nel.org, leonro@...dia.com,
        kwankhede@...dia.com, mgurtovoy@...dia.com, maorg@...dia.com,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH V2 mlx5-next 12/14] vfio/mlx5: Implement vfio_pci driver
 for mlx5 devices

* Jason Gunthorpe (jgg@...dia.com) wrote:
> On Mon, Oct 25, 2021 at 07:47:29PM +0100, Dr. David Alan Gilbert wrote:
> 
> > It may need some further refinement; for example in that quiesed state
> > do counters still tick? will a NIC still respond to packets that don't
> > get forwarded to the host?
> 
> At least for the mlx5 NIC the two states are 'able to issue outbound
> DMA' and 'all internal memories and state are frozen and unchanging'.

Yeh, so my point was just that if you're adding a new state to this
process, you need to define the details like that.

Dave

> The later means it should not respond/count/etc to network packets
> either.
> 
> Roughly it is
>  'able to mutate external state' / 'able to mutate internal state'
> 
> The invariant should be that successive calls to serialize the
> internal state while frozen should return the same serialization.
> 
> We may find that migratable PCI functions must have some limited
> functionality. Ie anything with a realtime compoment - for instance a
> sync-ethernet clock synchronization control loop, may become
> challenging to migrate without creating a serious functional
> distortion.
> 
> Jason
> 
-- 
Dr. David Alan Gilbert / dgilbert@...hat.com / Manchester, UK