Re: [virtio-dev] [PATCH v4] content: Introduce VIRTIO_NET_F_STANDBY feature

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Dec 10, 2018 at 05:34:53PM +0200, Sameeh Jubran wrote:
> On Mon, Dec 10, 2018 at 5:13 PM Sameeh Jubran <sameeh@daynix.com> wrote:
> >
> > On Sat, Dec 8, 2018 at 3:54 AM si-wei liu <si-wei.liu@oracle.com> wrote:
> > >
> > >
> > >
> > > On 12/05/2018 08:18 AM, Sameeh Jubran wrote:
> > > > Hi all,
> > > >
> > > > This is a followup on the discussion in the DPDK and Virtio monthly meeting.
> > > >
> > > > Michael suggested that layer 2 tests should be created in order to
> > > > test the PF/VF behavior in different scenarios without using VMs at
> > > > all which should speed up the testing process.
> > > >
> > > > The following "mausezahn" tool - which is part of netsniff-ng package
> > > > - can be used in order to generate layer 2 packets as follows:
> > > >
> > > > mausezahn enp59s0 -c 0 -a rand -b 20:71:c6:2a:68:38 "08 00 aa bb cc dd"
> > > >
> > > > The packets can be sniffed using tcpdump or netsniff-ng.
> > > Does tcpdump or netsniff-ng enable NIC's promiscuous mode by default?
> > > Try disable it when you monitor/capture the L2 packets.
> > netsniff-ng enables promiscuous mode by default, however the -M flag
> > can disable this.
> >
> > >
> > > >
> > > > I am not completely sure how the setup should look like on the host,
> > > > but here is a script which assigns macvlan to the PF and sets it's mac
> > > > address to be the same as the VF mac address. The scripts assumes that
> > > > the sriov is already configured and the vf are present.
> > > >
> > > > [root@wsfd-advnetlab10 ~]# cat go_macvlan.sh
> > > > MACVLAN_NAME=macvlan0
> > > > PF_NAME=enp59s0
> > > > VF_NUMBER=1
> > > > MAC_ADDR=20:71:c6:2a:68:38
> > > >
> > > > echo "$PF_NAME vf status before setting mac"
> > > > ip link show dev $PF_NAME
> > > > ip link set $PF_NAME vf $VF_NUMBER mac $MAC_ADDR
> > > > ip li add link $PF_NAME $MACVLAN_NAME address $MAC_ADDR type macvlan
> > > > ip link set $PF_NAME up
> > > > echo "$PF_NAME vf status after setting mac"
> > > > ip link show dev $PF_NAME
> > > >
> > > > Please share your thoughts on how the different test scenarios should
> > > > go, I can customize the scripts further more and host them somewhere.
> > > You can do something like below:
> > >
> > > FAKE_VLAN=123
> > > ip link set $MACVLAN_NAME up
> > > ip link set $PF_NAME vf $VF_NUMBER vlan $FAKE_VLAN
> > >
> > > Datapath now switched to macvlan0, which should get the L2 packets from
> > > over the wire.
> > >
> > > ip link set $PF_NAME vf $VF_NUMBER vlan 0
> > > ip link set $MACVLAN_NAME down
> > >
> > > Datapath now switched back to VF. VF#1 should get packets.
> > >
> > > For a more accurate downtime test, replace 'ip link set vf .. vlan ...'
> > > to unbind VF from the original driver and bind it to vfio-pci.
> > Yup.
> 
> The only issue that I'm not sure on how to deal with, is how to listen
> to the packets on the vf. How can I make sure that they are arriving
> there?

Using --dev flag to bind to the vf device?


> > >
> > >
> > > Regards,
> > > -Siwei
> > >
> > > >
> > > > On Tue, Dec 4, 2018 at 5:59 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > >> On Mon, Dec 03, 2018 at 06:09:19PM -0800, si-wei liu wrote:
> > > >>>> I agree. But a single flag is not much of an extension. We don't even
> > > >>>> need it in netlink, can be anywhere in e.g. sysfs.
> > > >>> I think sysfs attribute is for exposing the capability, while you still need
> > > >>> to set up macvtap with some special mode via netlink. That way it doesn't
> > > >>> break current behavior, and when VF's MAC filter is added macvtap would need
> > > >>> to react to remove the filter from NIC. And add the one back when VF's MAC
> > > >>> is removed.
> > > >> All this will be up to the developers actually working on it. My
> > > >> understanding is that intel is going to just change the behaviour
> > > >> unconditionally, and it's already the case for Mellanox.
> > > >> That creates a critical mass large enough that maybe others
> > > >> just need to confirm.
> > > >>
> > > >> ...
> > > >>
> > > >>
> > > >>>> Meanwhile what's missing and was missing all along for the change you
> > > >>>> seem to be advocating for to get off the ground is people who
> > > >>>> are ready to actually send e.g. spec, guest driver, test patches.
> > > >>> Partly because it hadn't been converged to the best way to do it (even the
> > > >>> group ID mechanism with PCI bridge can address our need you don't seem to
> > > >>> think it is valuable). The in-kernel approach is fine at its appearance, but
> > > >>> I personally don't believe changing every legacy driver is the way to go.
> > > >>> It's the choice of implementation and what has been implemented in those
> > > >>> drivers today IMHO is nothing wrong.
> > > >> It's not a question of being wrong as such.
> > > >> A standard behaviour is clearly better than each driver doing its
> > > >> own thing which is the case now. As long as we ar standardizing,
> > > >> let's standardize on something that matches our needs?
> > > >> But I really see no problem with also supporting other options,
> > > >> as long as someone is prepared to actually put in the work.
> > > >>
> > > >>
> > > >>>>>>     Still this assumes just creating a VF
> > > >>>>>> doesn't yet program the on-card filter to cause packet drops.
> > > >>>>> Suppose this behavior is fixable in legacy Intel NIC, you would still need
> > > >>>>> to evacuate the filter programmed by macvtap previously when VF's filter
> > > >>>>> gets activated (typically when VF's netdev is netif_running() in a Linux
> > > >>>>> guest). That's what we and NetVSC call as "datapath switching", and where
> > > >>>>> this could be handled (driver, net core, or userspace) is the core for the
> > > >>>>> architectural design that I spent much time on.
> > > >>>>>
> > > >>>>> Having said it, I don't expect or would desperately wait on one vendor to
> > > >>>>> fix a legacy driver which wasn't quite motivated, then no work would be done
> > > >>>>> on that.
> > > >>>> Then that device can't be used with the mechanism in question.
> > > >>>> Or if there are lots of drivers like this maybe someone will be
> > > >>>> motivated enough to post a better implementation with a new
> > > >>>> feature bit. It's not that I'm arguing against that.
> > > >>>>
> > > >>>> But given the options of teaching management to play with
> > > >>>> netlink API in response to guest actions, and with VCPU stopped,
> > > >>>> and doing it all in host kernel drivers, I know I'll prefer host kernel
> > > >>>> changes.
> > > >>> We have some internal patches that leverage management to respond to various
> > > >>> guest actions. If you're interested we can post them. The thing is no one
> > > >>> would like to work on the libvirt changes, while internally we have our own
> > > >>> orchestration software which is not libvirt. But if you think it's fine we
> > > >>> can definitely share our QEMU patches while leaving out libvirt.
> > > >>>
> > > >>> Thanks,
> > > >>> -Siwei
> > > >> Sure, why not.
> > > >>
> > > >> The following is generally necessary for any virtio project to happen:
> > > >> - guest patches
> > > >> - qemu patches
> > > >> - spec documentation
> > > >>
> > > >> Some extras are sometimes a dependency, e.g. host kernel patches.
> > > >>
> > > >>
> > > >> Typically at least two of these are enough for people to
> > > >> be able to figure out how things work.
> > > >>
> > > >>
> > > >>
> > > >>
> > > >>>>> If you'd go the way, please make sure Intel could change their
> > > >>>>> driver first.
> > > >>>> We'll see what happens with that. It's Sridhar from intel that implemented
> > > >>>> the guest changes after all, so I expect he's motivated to make them
> > > >>>> work well.
> > > >>>>
> > > >>>>
> > > >>>>>>     Let's
> > > >>>>>> assume drivers are fixed to do that. How does userspace know
> > > >>>>>> that's the case? We might need some kind of attribute so
> > > >>>>>> userspace can detect it.
> > > >>>>> Where do you envision the new attribute could be at? Supposedly it'd be
> > > >>>>> exposed by the kernel, which constitutes a new API or API changes.
> > > >>>>>
> > > >>>>>
> > > >>>>> Thanks,
> > > >>>>> -Siwei
> > > >>>> People add e.g. new attributes in sysfs left and right.  It's unlikely
> > > >>>> to be a matter of serious contention.
> > > >>>>
> > > >>>>>>>> Question is how does userspace know driver isn't broken in this respect?
> > > >>>>>>>> Let's add a "vf failover" flag somewhere so this can be probed?
> > > >>>>>>>>
> > > >>>> ---------------------------------------------------------------------
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> > > >>>>
> > > >
> > > >
> > >
> >
> >
> > --
> > Respectfully,
> > Sameeh Jubran
> > Linkedin
> > Software Engineer @ Daynix.
> 
> 
> 
> -- 
> Respectfully,
> Sameeh Jubran
> Linkedin
> Software Engineer @ Daynix.

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