Samudrala, Sridhar
2018-Jun-13 00:08 UTC
[virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net
On 6/12/2018 4:34 AM, Michael S. Tsirkin wrote:> On Mon, Jun 11, 2018 at 10:02:45PM -0700, Samudrala, Sridhar wrote: >> On 6/11/2018 7:17 PM, Michael S. Tsirkin wrote: >>> On Tue, Jun 12, 2018 at 09:54:44AM +0800, Jason Wang wrote: >>>> On 2018?06?12? 01:26, Michael S. Tsirkin wrote: >>>>> On Mon, May 07, 2018 at 04:09:54PM -0700, Sridhar Samudrala wrote: >>>>>> This feature bit can be used by hypervisor to indicate virtio_net device to >>>>>> act as a standby for another device with the same MAC address. >>>>>> >>>>>> I tested this with a small change to the patch to mark the STANDBY feature 'true' >>>>>> by default as i am using libvirt to start the VMs. >>>>>> Is there a way to pass the newly added feature bit 'standby' to qemu via libvirt >>>>>> XML file? >>>>>> >>>>>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com> >>>>> So I do not think we can commit to this interface: we >>>>> really need to control visibility of the primary device. >>>> The problem is legacy guest won't use primary device at all if we do this. >>> And that's by design - I think it's the only way to ensure the >>> legacy guest isn't confused. >> Yes. I think so. But i am not sure if Qemu is the right place to control the visibility >> of the primary device. The primary device may not be specified as an argument to Qemu. It >> may be plugged in later. >> The cloud service provider is providing a feature that enables low latency datapath and live >> migration capability. >> A tenant can use this feature only if he is running a VM that has virtio-net with failover support. > Well live migration is there already. The new feature is low latency > data path.we get live migration with just virtio. But I meant live migration with VF as primary device.> > And it's the guest that needs failover support not the VM.Isn't guest and VM synonymous?> > >> I think Qemu should check if guest virtio-net supports this feature and provide a mechanism for >> an upper layer indicating if the STANDBY feature is successfully negotiated or not. >> The upper layer can then decide if it should hot plug a VF with the same MAC and manage the 2 links. >> If VF is successfully hot plugged, virtio-net link should be disabled. > Did you even talk to upper layer management about it? > Just list the steps they need to do and you will see > that's a lot of machinery to manage by the upper layer. > > What do we gain in flexibility? As far as I can see the > only gain is some resources saved for legacy VMs. > > That's not a lot as tenant of the upper layer probably already has > at least a hunch that it's a new guest otherwise > why bother specifying the feature at all - you > save even more resources without it. >I am not all that familiar with how Qemu manages network devices. If we can do all the required management of the primary/standby devices within Qemu, that is definitely a better approach without upper layer involvement.> > >>>> How about control the visibility of standby device? >>>> >>>> Thanks >>> standy the always there to guarantee no downtime. >>> >>>>> However just for testing purposes, we could add a non-stable >>>>> interface "x-standby" with the understanding that as any >>>>> x- prefix it's unstable and will be changed down the road, >>>>> likely in the next release. >>>>> >>>>> >>>>>> --- >>>>>> hw/net/virtio-net.c | 2 ++ >>>>>> include/standard-headers/linux/virtio_net.h | 3 +++ >>>>>> 2 files changed, 5 insertions(+) >>>>>> >>>>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c >>>>>> index 90502fca7c..38b3140670 100644 >>>>>> --- a/hw/net/virtio-net.c >>>>>> +++ b/hw/net/virtio-net.c >>>>>> @@ -2198,6 +2198,8 @@ static Property virtio_net_properties[] = { >>>>>> true), >>>>>> DEFINE_PROP_INT32("speed", VirtIONet, net_conf.speed, SPEED_UNKNOWN), >>>>>> DEFINE_PROP_STRING("duplex", VirtIONet, net_conf.duplex_str), >>>>>> + DEFINE_PROP_BIT64("standby", VirtIONet, host_features, VIRTIO_NET_F_STANDBY, >>>>>> + false), >>>>>> DEFINE_PROP_END_OF_LIST(), >>>>>> }; >>>>>> diff --git a/include/standard-headers/linux/virtio_net.h b/include/standard-headers/linux/virtio_net.h >>>>>> index e9f255ea3f..01ec09684c 100644 >>>>>> --- a/include/standard-headers/linux/virtio_net.h >>>>>> +++ b/include/standard-headers/linux/virtio_net.h >>>>>> @@ -57,6 +57,9 @@ >>>>>> * Steering */ >>>>>> #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */ >>>>>> +#define VIRTIO_NET_F_STANDBY 62 /* Act as standby for another device >>>>>> + * with the same MAC. >>>>>> + */ >>>>>> #define VIRTIO_NET_F_SPEED_DUPLEX 63 /* Device set linkspeed and duplex */ >>>>>> #ifndef VIRTIO_NET_NO_LEGACY >>>>>> -- >>>>>> 2.14.3 > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe at lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help at lists.oasis-open.org >
Siwei Liu
2018-Jun-14 01:02 UTC
[virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net
On Tue, Jun 12, 2018 at 5:08 PM, Samudrala, Sridhar <sridhar.samudrala at intel.com> wrote:> On 6/12/2018 4:34 AM, Michael S. Tsirkin wrote: >> >> On Mon, Jun 11, 2018 at 10:02:45PM -0700, Samudrala, Sridhar wrote: >>> >>> On 6/11/2018 7:17 PM, Michael S. Tsirkin wrote: >>>> >>>> On Tue, Jun 12, 2018 at 09:54:44AM +0800, Jason Wang wrote: >>>>> >>>>> On 2018?06?12? 01:26, Michael S. Tsirkin wrote: >>>>>> >>>>>> On Mon, May 07, 2018 at 04:09:54PM -0700, Sridhar Samudrala wrote: >>>>>>> >>>>>>> This feature bit can be used by hypervisor to indicate virtio_net >>>>>>> device to >>>>>>> act as a standby for another device with the same MAC address. >>>>>>> >>>>>>> I tested this with a small change to the patch to mark the STANDBY >>>>>>> feature 'true' >>>>>>> by default as i am using libvirt to start the VMs. >>>>>>> Is there a way to pass the newly added feature bit 'standby' to qemu >>>>>>> via libvirt >>>>>>> XML file? >>>>>>> >>>>>>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com> >>>>>> >>>>>> So I do not think we can commit to this interface: we >>>>>> really need to control visibility of the primary device. >>>>> >>>>> The problem is legacy guest won't use primary device at all if we do >>>>> this. >>>> >>>> And that's by design - I think it's the only way to ensure the >>>> legacy guest isn't confused. >>> >>> Yes. I think so. But i am not sure if Qemu is the right place to control >>> the visibility >>> of the primary device. The primary device may not be specified as an >>> argument to Qemu. It >>> may be plugged in later. >>> The cloud service provider is providing a feature that enables low >>> latency datapath and live >>> migration capability. >>> A tenant can use this feature only if he is running a VM that has >>> virtio-net with failover support. >> >> Well live migration is there already. The new feature is low latency >> data path. > > > we get live migration with just virtio. But I meant live migration with VF > as > primary device. > >> >> And it's the guest that needs failover support not the VM. > > > Isn't guest and VM synonymous? > > >> >> >>> I think Qemu should check if guest virtio-net supports this feature and >>> provide a mechanism for >>> an upper layer indicating if the STANDBY feature is successfully >>> negotiated or not. >>> The upper layer can then decide if it should hot plug a VF with the same >>> MAC and manage the 2 links. >>> If VF is successfully hot plugged, virtio-net link should be disabled. >> >> Did you even talk to upper layer management about it? >> Just list the steps they need to do and you will see >> that's a lot of machinery to manage by the upper layer. >> >> What do we gain in flexibility? As far as I can see the >> only gain is some resources saved for legacy VMs. >> >> That's not a lot as tenant of the upper layer probably already has >> at least a hunch that it's a new guest otherwise >> why bother specifying the feature at all - you >> save even more resources without it. >> > > I am not all that familiar with how Qemu manages network devices. If we can > do all the > required management of the primary/standby devices within Qemu, that is > definitely a better > approach without upper layer involvement.Right. I would imagine in the extreme case the upper layer doesn't have to be involved at all if QEMU manages all hot plug/unplug logic. The management tool can supply passthrough device and virtio with the same group UUID, QEMU auto-manages the presence of the primary, and hot plug the device as needed before or after the migration. -Siwei> > >> >> >>>>> How about control the visibility of standby device? >>>>> >>>>> Thanks >>>> >>>> standy the always there to guarantee no downtime. >>>> >>>>>> However just for testing purposes, we could add a non-stable >>>>>> interface "x-standby" with the understanding that as any >>>>>> x- prefix it's unstable and will be changed down the road, >>>>>> likely in the next release. >>>>>> >>>>>> >>>>>>> --- >>>>>>> hw/net/virtio-net.c | 2 ++ >>>>>>> include/standard-headers/linux/virtio_net.h | 3 +++ >>>>>>> 2 files changed, 5 insertions(+) >>>>>>> >>>>>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c >>>>>>> index 90502fca7c..38b3140670 100644 >>>>>>> --- a/hw/net/virtio-net.c >>>>>>> +++ b/hw/net/virtio-net.c >>>>>>> @@ -2198,6 +2198,8 @@ static Property virtio_net_properties[] = { >>>>>>> true), >>>>>>> DEFINE_PROP_INT32("speed", VirtIONet, net_conf.speed, >>>>>>> SPEED_UNKNOWN), >>>>>>> DEFINE_PROP_STRING("duplex", VirtIONet, net_conf.duplex_str), >>>>>>> + DEFINE_PROP_BIT64("standby", VirtIONet, host_features, >>>>>>> VIRTIO_NET_F_STANDBY, >>>>>>> + false), >>>>>>> DEFINE_PROP_END_OF_LIST(), >>>>>>> }; >>>>>>> diff --git a/include/standard-headers/linux/virtio_net.h >>>>>>> b/include/standard-headers/linux/virtio_net.h >>>>>>> index e9f255ea3f..01ec09684c 100644 >>>>>>> --- a/include/standard-headers/linux/virtio_net.h >>>>>>> +++ b/include/standard-headers/linux/virtio_net.h >>>>>>> @@ -57,6 +57,9 @@ >>>>>>> * Steering */ >>>>>>> #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */ >>>>>>> +#define VIRTIO_NET_F_STANDBY 62 /* Act as standby for >>>>>>> another device >>>>>>> + * with the same MAC. >>>>>>> + */ >>>>>>> #define VIRTIO_NET_F_SPEED_DUPLEX 63 /* Device set >>>>>>> linkspeed and duplex */ >>>>>>> #ifndef VIRTIO_NET_NO_LEGACY >>>>>>> -- >>>>>>> 2.14.3 >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: virtio-dev-unsubscribe at lists.oasis-open.org >> For additional commands, e-mail: virtio-dev-help at lists.oasis-open.org >> >
Cornelia Huck
2018-Jun-14 10:02 UTC
[virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net
I've been pointed to this discussion (which I had missed previously) and I'm getting a headache. Let me first summarize how I understand how this feature is supposed to work, then I'll respond to some individual points. The basic idea is to enable guests to migrate seamlessly, while still making it possible for them to use a passed-through device for more performance etc. The means to do so is to hook a virtio-net device together with a network device passed through via vfio. The vfio-handled device is there for performance, the virtio device for migratability. We have a new virtio feature bit for that which needs to be negotiated for that 'combined' device to be available. We have to consider two cases: - Older guests that do not support the new feature bit. We presume that those guests will be confused if they get two network devices with the same MAC, so the idea is to not show them the vfio-handled device at all. - Guests that negotiate the feature bit. We only know positively that they (a) know the feature bit and (b) are prepared to handle the consequences of negotiating it after they set the FEATURES_OK bit. This is therefore the earliest point in time that the vfio-handled device should be visible or usable for the guest. On Wed, 13 Jun 2018 18:02:01 -0700 Siwei Liu <loseweigh at gmail.com> wrote:> On Tue, Jun 12, 2018 at 5:08 PM, Samudrala, Sridhar > <sridhar.samudrala at intel.com> wrote: > > On 6/12/2018 4:34 AM, Michael S. Tsirkin wrote: > >> > >> On Mon, Jun 11, 2018 at 10:02:45PM -0700, Samudrala, Sridhar wrote: > >>> > >>> On 6/11/2018 7:17 PM, Michael S. Tsirkin wrote: > >>>> > >>>> On Tue, Jun 12, 2018 at 09:54:44AM +0800, Jason Wang wrote: > >>>>> > >>>>> On 2018?06?12? 01:26, Michael S. Tsirkin wrote: > >>>>>> > >>>>>> On Mon, May 07, 2018 at 04:09:54PM -0700, Sridhar Samudrala wrote: > >>>>>>> > >>>>>>> This feature bit can be used by hypervisor to indicate virtio_net > >>>>>>> device to > >>>>>>> act as a standby for another device with the same MAC address. > >>>>>>> > >>>>>>> I tested this with a small change to the patch to mark the STANDBY > >>>>>>> feature 'true' > >>>>>>> by default as i am using libvirt to start the VMs. > >>>>>>> Is there a way to pass the newly added feature bit 'standby' to qemu > >>>>>>> via libvirt > >>>>>>> XML file? > >>>>>>> > >>>>>>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com> > >>>>>> > >>>>>> So I do not think we can commit to this interface: we > >>>>>> really need to control visibility of the primary device. > >>>>> > >>>>> The problem is legacy guest won't use primary device at all if we do > >>>>> this. > >>>> > >>>> And that's by design - I think it's the only way to ensure the > >>>> legacy guest isn't confused. > >>> > >>> Yes. I think so. But i am not sure if Qemu is the right place to control > >>> the visibility > >>> of the primary device. The primary device may not be specified as an > >>> argument to Qemu. It > >>> may be plugged in later. > >>> The cloud service provider is providing a feature that enables low > >>> latency datapath and live > >>> migration capability. > >>> A tenant can use this feature only if he is running a VM that has > >>> virtio-net with failover support.So, do you know from the outset that there will be such a coupled device? I.e., is it a property of the VM definition? Can there be a 'prepared' virtio-net device that presents the STANDBY feature even if there currently is no vfio-handled device available -- but making it possible to simply hotplug that device later? Should it be possible to add a virtio/vfio pair later on?> >> > >> Well live migration is there already. The new feature is low latency > >> data path. > > > > > > we get live migration with just virtio. But I meant live migration with VF > > as > > primary device. > > > >> > >> And it's the guest that needs failover support not the VM. > > > > > > Isn't guest and VM synonymous?I think we need to be really careful to not mix up the two: The VM contains the definitions, but it is up to the guest how it uses them.> > > > > >> > >> > >>> I think Qemu should check if guest virtio-net supports this feature and > >>> provide a mechanism for > >>> an upper layer indicating if the STANDBY feature is successfully > >>> negotiated or not. > >>> The upper layer can then decide if it should hot plug a VF with the same > >>> MAC and manage the 2 links. > >>> If VF is successfully hot plugged, virtio-net link should be disabled. > >> > >> Did you even talk to upper layer management about it? > >> Just list the steps they need to do and you will see > >> that's a lot of machinery to manage by the upper layer. > >> > >> What do we gain in flexibility? As far as I can see the > >> only gain is some resources saved for legacy VMs. > >> > >> That's not a lot as tenant of the upper layer probably already has > >> at least a hunch that it's a new guest otherwise > >> why bother specifying the feature at all - you > >> save even more resources without it. > >> > > > > I am not all that familiar with how Qemu manages network devices. If we can > > do all the > > required management of the primary/standby devices within Qemu, that is > > definitely a better > > approach without upper layer involvement. > > Right. I would imagine in the extreme case the upper layer doesn't > have to be involved at all if QEMU manages all hot plug/unplug logic. > The management tool can supply passthrough device and virtio with the > same group UUID, QEMU auto-manages the presence of the primary, and > hot plug the device as needed before or after the migration.I do not really see how you can manage that kind of stuff in QEMU only. Have you talked to some libvirt folks? (And I'm not sure what you refer to with 'group UUID'?) Also, I think you need to make a distinction between hotplugging a device and making it visible to the guest. What does 'hotplugging' mean here? Adding it to the VM definition? Would it be enough to have the vfio-based device not operational until the virtio feature bit has been negotiated? What happens if the guest does not use the vfio-based device after it has been made available? Will you still disable the virtio-net link? (All that link handling definitely sounds like a task for libvirt or the like.) Regarding hot(un)plugging during migration, I think you also need to keep in mind that different architectures/busses have different semantics there. Something that works if there's an unplug handshake may not work on a platform with surprise removal. Have you considered guest agents? All of this is punching through several layers, and I'm not sure if that is a good idea.
Michael S. Tsirkin
2018-Jun-14 12:50 UTC
[virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net
On Wed, Jun 13, 2018 at 06:02:01PM -0700, Siwei Liu wrote:> >> And it's the guest that needs failover support not the VM. > > > > > > Isn't guest and VM synonymous?Guest is whatever software is running on top of the hypervisor. The virtual machine is the interface between the two. -- MST