Re: [virtio-comment] Re: [virtio-dev] Re: [virtio-comment] Re: [PATCH v7] virtio-net: support inner header hash

[Jason Wang <jasowang@redhat.com>]

On Wed, Jan 11, 2023 at 11:23 AM Heng Qi <hengqi@linux.alibaba.com> wrote:
>
>
>
> å 2023/1/10 äå3:26, Heng Qi åé:
> > On Tue, Jan 10, 2023 at 12:57:38AM -0500, Michael S. Tsirkin wrote:
> >> On Tue, Jan 10, 2023 at 12:25:02AM -0500, Michael S. Tsirkin wrote:
> >>>> This will give extra pressure on the management stack, e.g it requires
> >>>> the device to have an out of spec way for introspection.
> >>>>
> >>>> Thanks
> >>> As I tried to explain this is already the case. Feature bits do not
> >>> describe device capabilities fully, some of them are in config space.

Yes.

> >> To be precise, this does not necessarily require introspection, but
> >> it does require management control over config space
> >> such as supported hash types just like it has control over feature bits.
> >> E.g. QEMU currently seems to hard-code these to
> >> #define VIRTIO_NET_RSS_SUPPORTED_HASHES (VIRTIO_NET_RSS_HASH_TYPE_IPv4 | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_TCPv4 | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_IPv6 | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_TCPv6 | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_UDPv6 | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_IP_EX | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_TCP_EX | \
> >>                                           VIRTIO_NET_RSS_HASH_TYPE_UDP_EX)
> >>
> >> but there's no reason not to give management control over these.

Note that the management expects the migration compatibility to work
with machine types. So it needs a way to disable some tunnel hash
types to make it work for old machine types.

> > Yes, QEMU has requirements for live migration: the PCI config space will be
> > checked in get_pci_config_device(), and if src and dst are inconsistent, it
> > will prompt that the live migration failed.

It might be too late since it can't work for the second run (unlike subsection).

>
> To be clearer, I mean \filed{supported_hash_types} in structure
> virtio_net_config.

Yes.

Thanks

>
> Thanks.
>
> > In fact, this is also done within our group. Live migration requires that
> > the two VMs have the same rss configuration, otherwise the migration will fail.
> >
> > Therefore, it seems that we can regularize the description of VIRTIO_NET_F_HASH_TUNNEL into
> > "[VIRTIO_NET_F_HASH_TUNNEL(52)] Device supports inner header hash for tunnel-encapsulated packets.",
> > and use different hash_types to help the migration determine whether it can succeed.
> >
> > Thanks.
> >
> >> --
> >> MST
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