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Subject: Re: [virtio-comment] Re: [PATCH V2 4/6] virtio-pci: implement VIRTIO_F_QUEUE_STATE
On Wed, Nov 22, 2023 at 09:32:53AM +0800, Zhu, Lingshan wrote: > > > On 11/17/2023 6:45 PM, Michael S. Tsirkin wrote: > > On Fri, Nov 17, 2023 at 06:02:14PM +0800, Zhu, Lingshan wrote: > > > > > > On 11/16/2023 6:21 PM, Parav Pandit wrote: > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > Sent: Thursday, November 16, 2023 3:45 PM > > > > > > > > > > On 11/16/2023 1:35 AM, Parav Pandit wrote: > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > > > Sent: Monday, November 13, 2023 2:56 PM > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 11/10/2023 8:31 PM, Parav Pandit wrote: > > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > > > > > Sent: Friday, November 10, 2023 1:22 PM > > > > > > > > > > > > > > > > > > > > > > > > > > > On 11/9/2023 6:25 PM, Parav Pandit wrote: > > > > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > > > > > > > Sent: Thursday, November 9, 2023 3:39 PM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 11/9/2023 2:28 PM, Parav Pandit wrote: > > > > > > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > > > > > > > > > Sent: Tuesday, November 7, 2023 3:02 PM > > > > > > > > > > > > > > > > > > > > > > > > > > On 11/6/2023 6:52 PM, Parav Pandit wrote: > > > > > > > > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > > > > > > > > > > > Sent: Monday, November 6, 2023 2:57 PM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 11/6/2023 12:12 PM, Parav Pandit wrote: > > > > > > > > > > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > > > > > > > > > > > > > Sent: Monday, November 6, 2023 9:01 AM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 11/3/2023 11:50 PM, Parav Pandit wrote: > > > > > > > > > > > > > > > > > > > From: virtio-comment@lists.oasis-open.org > > > > > > > > > > > > > > > > > > > <virtio-comment@lists.oasis- open.org> On Behalf Of Zhu, > > > > > > > > > > > > > > > > > > > Lingshan > > > > > > > > > > > > > > > > > > > Sent: Friday, November 3, 2023 8:27 PM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 11/3/2023 7:35 PM, Parav Pandit wrote: > > > > > > > > > > > > > > > > > > > > > From: Zhu Lingshan <lingshan.zhu@intel.com> > > > > > > > > > > > > > > > > > > > > > Sent: Friday, November 3, 2023 4:05 PM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > This patch adds two new le16 fields to common > > > > > > > > > > > > > > > > > > > > > configuration structure to support VIRTIO_F_QUEUE_STATE > > > > > > > > > > > > > > > > > > > > > in PCI transport > > > > > > > > > layer. > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com> > > > > > > > > > > > > > > > > > > > > > --- > > > > > > > > > > > > > > > > > > > > > transport-pci.tex | 18 ++++++++++++++++++ > > > > > > > > > > > > > > > > > > > > > 1 file changed, 18 insertions(+) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/transport-pci.tex b/transport-pci.tex > > > > > > > > > > > > > > > > > > > > > index > > > > > > > > > > > > > > > > > > > > > a5c6719..3161519 100644 > > > > > > > > > > > > > > > > > > > > > --- a/transport-pci.tex > > > > > > > > > > > > > > > > > > > > > +++ b/transport-pci.tex > > > > > > > > > > > > > > > > > > > > > @@ -325,6 +325,10 @@ \subsubsection{Common > > > > > > > configuration > > > > > > > > > > > > > > > > > structure > > > > > > > > > > > > > > > > > > > > > layout}\label{sec:Virtio Transport > > > > > > > > > > > > > > > > > > > > > /* About the administration virtqueue. */ > > > > > > > > > > > > > > > > > > > > > le16 admin_queue_index; /* read-only for > > > > > driver > > > > > > > > > */ > > > > > > > > > > > > > > > > > > > > > le16 admin_queue_num; /* read-only for > > > > > driver > > > > > > > > > */ > > > > > > > > > > > > > > > > > > > > > + > > > > > > > > > > > > > > > > > > > > > + /* Virtqueue state */ > > > > > > > > > > > > > > > > > > > > > + le16 queue_avail_state; /* read-write */ > > > > > > > > > > > > > > > > > > > > > + le16 queue_used_state; /* read-write */ > > > > > > > > > > > > > > > > > > > > This tiny interface for 128 virtio net queues through > > > > > > > > > > > > > > > > > > > > register read writes, does > > > > > > > > > > > > > > > > > > > not work effectively. > > > > > > > > > > > > > > > > > > > > There are inflight out of order descriptors for block also. > > > > > > > > > > > > > > > > > > > > Hence toy registers like this do not work. > > > > > > > > > > > > > > > > > > > Do you know there is a queue_select? Why this does not > > > > > work? > > > > > > > > > > > > > > > > > > > Do you know how other queue related fields work? > > > > > > > > > > > > > > > > > > :) > > > > > > > > > > > > > > > > > > Yes. If you notice queue_reset related critical spec bug > > > > > > > > > > > > > > > > > > fix was done when it > > > > > > > > > > > > > > > > > was introduced so that live migration can _actually_ work. > > > > > > > > > > > > > > > > > > When queue_select is done for 128 queues serially, it take > > > > > > > > > > > > > > > > > > a lot of time to > > > > > > > > > > > > > > > > > read those slow register interface for this + inflight > > > > > > > > > > > > > > > > > descriptors + > > > > > > > > > more. > > > > > > > > > > > > > > > > > interesting, virtio work in this pattern for many years, right? > > > > > > > > > > > > > > > > All these years 400Gbps and 800Gbps virtio was not present, > > > > > > > > > > > > > > > > number of > > > > > > > > > > > > > > > queues were not in hw. > > > > > > > > > > > > > > > The registers are control path in config space, how 400G or > > > > > > > > > > > > > > > 800G > > > > > > > > > affect?? > > > > > > > > > > > > > > Because those are the one in practice requires large number of VQs. > > > > > > > > > > > > > > > > > > > > > > > > > > > > You are asking per VQ register commands to modify things > > > > > > > > > > > > > > dynamically via > > > > > > > > > > > > > this one vq at a time, serializing all the operations. > > > > > > > > > > > > > > It does not scale well with high q count. > > > > > > > > > > > > > This is not dynamically, it only happens when SUSPEND and RESUME. > > > > > > > > > > > > > This is the same mechanism how virtio initialize a virtqueue, > > > > > > > > > > > > > working for many years. > > > > > > > > > > > > No. when virtio driver initializes it for the first time, there > > > > > > > > > > > > is no active traffic > > > > > > > > > > > that gets lost. > > > > > > > > > > > > This is because the interface is not yet up and not part of the > > > > > > > > > > > > network > > > > > > > yet. > > > > > > > > > > > > The resume must be fast enough, because the remote node is > > > > > > > > > > > > sending > > > > > > > > > > > packets. > > > > > > > > > > > > Hence it is different from driver init time queue enable. > > > > > > > > > > > I am not sure any packets arrive before a link announce at the > > > > > > > > > > > destination > > > > > > > > > side. > > > > > > > > > > I think it can. > > > > > > > > > > Because there is no notification of member device link down > > > > > > > > > > intimation to > > > > > > > > > remote side. > > > > > > > > > > The L4 and L5 protocols have no knowledge that node which they are > > > > > > > > > interacting is behind some layers of switches. > > > > > > > > > > So keeping this time low is desired. > > > > > > > > > The NIC should broad cast itself first, so that other peers in the > > > > > > > > > network know(for example its mac to route it) how to send a message to > > > > > it. > > > > > > > > > This is necessary, for example VIRTIO_NET_F_GUEST_ANNOUNCE, similar > > > > > > > > > mechanism work for in-marketing productions for years. > > > > > > > > > > > > > > > > > > This is out of the topic anyway. > > > > > > > > > > > > > > > See the virtio common cfg, you will find the max number of > > > > > > > > > > > > > > > vqs is there, num_queues. > > > > > > > > > > > > > > :) > > > > > > > > > > > > > > Sure. those values at high q count affects. > > > > > > > > > > > > > the driver need to initialize them anyway. > > > > > > > > > > > > That is before the traffic starts from remote end. > > > > > > > > > > > see above, that needs a link announce and this is after > > > > > > > > > > > re-initialization > > > > > > > > > > > > > > > > Device didnât support LM. > > > > > > > > > > > > > > > > Many limitations existed all these years and TC is improving > > > > > > > > > > > > > > > > and expanding > > > > > > > > > > > > > > > them. > > > > > > > > > > > > > > > > So all these years do not matter. > > > > > > > > > > > > > > > Not sure what are you talking about, haven't we initialize > > > > > > > > > > > > > > > the device and vqs in config space for years?????? What's > > > > > > > > > > > > > > > wrong with this > > > > > > > > > > > mechanism? > > > > > > > > > > > > > > > Are you questioning virito-pci fundamentals??? > > > > > > > > > > > > > > Donât point to in-efficient past to establish similar in-efficient future. > > > > > > > > > > > > > interesting, you know this is a one-time thing, right? > > > > > > > > > > > > > and you are aware of this has been there for years. > > > > > > > > > > > > > > > > > > > Like how to set a queue size and enable it? > > > > > > > > > > > > > > > > > > Those are meant to be used before DRIVER_OK stage as they > > > > > > > > > > > > > > > > > > are init time > > > > > > > > > > > > > > > > > registers. > > > > > > > > > > > > > > > > > > Not to keep abusing them.. > > > > > > > > > > > > > > > > > don't you need to set queue_size at the destination side? > > > > > > > > > > > > > > > > No. > > > > > > > > > > > > > > > > But the src/dst does not matter. > > > > > > > > > > > > > > > > Queue_size to be set before DRIVER_OK like rest of the > > > > > > > > > > > > > > > > registers, as all > > > > > > > > > > > > > > > queues must be created before the driver_ok phase. > > > > > > > > > > > > > > > > Queue_reset was last moment exception. > > > > > > > > > > > > > > > create a queue? Nvidia specific? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Huh. No. > > > > > > > > > > > > > > Do git log and realize what happened with queue_reset. > > > > > > > > > > > > > You didn't answer the question, does the spec even has defined > > > > > > > > > > > > > "create a > > > > > > > > > > > vq"? > > > > > > > > > > > > Enabled/created = tomato/tomato when discussing the spec in > > > > > > > > > > > > non-normative > > > > > > > > > > > email conversation. > > > > > > > > > > > > It's irrelevant. > > > > > > > > > > > Then lets not debate on this enable a vq or create a vq anymore > > > > > > > > > > > > All I am saying is, when we know the limitations of the > > > > > > > > > > > > transport and when industry is forwarding to not introduced more > > > > > > > > > > > > and more on-die register > > > > > > > > > > > for once in lifetime work of device migration, we just use the > > > > > > > > > > > optimal command and queue interface that is native to virtio. > > > > > > > > > > > PCI config space has its own limitations, and admin vq has its > > > > > > > > > > > advantages, but that does not apply to all use cases. > > > > > > > > > > > > > > > > > > > > > There was a recent work done emulating the SR-IOV cap and allowing > > > > > > > > > > VM to > > > > > > > > > enable SR-IOV in [1]. > > > > > > > > > > This is the option I mentioned few weeks ago. > > > > > > > > > > > > > > > > > > > > So with admin commands and admin virtqueues, even nested model > > > > > > > > > > will work > > > > > > > > > using [1]. > > > > > > > > > > [1] > > > > > > > > > > https://netdevconf.info/0x17/sessions/talk/unleashing-sr-iov-offlo > > > > > > > > > > ad > > > > > > > > > > -o > > > > > > > > > > n-virtual-machines.html > > > > > > > > > We should take this into consideration once it is standardized in > > > > > > > > > the spec, maybe not now, there can always be many workarounds to > > > > > > > > > solve one > > > > > > > problem. > > > > > > > > Sure, until that point the admin commands are able to suffice the need > > > > > well. > > > > > > > > And when the spec changes in transport occurs (if needed), current > > > > > > > > admin > > > > > > > command and admin vq also fits very well that will follow above [1]. > > > > > > > we have pointed lots of problems for admin vq based live migration > > > > > > > proposal, I won't repeat them here > > > > > > I donât see any. > > > > > > Nested is already solved using above. > > > > > I don't see how, do you mind to work out the patches? > > > > Once the base series is completed, nested cases can be addressed. > > > > I wont be able to work on the patches for it until we finish for the first level virtualization. > > > As you know, nested is supported well in current virtio, so please don't > > > break it. > > So for nesting, it seems cleaner to support sending commands through > > device itself. > I guess this requires per-VF admin vq or some agents & tricks. I suggested a gateway in the VF for this. Really more or less like what you did for write tracking except use the admin command format. We'll need a new group type which just includes device itself. > > You aren't going to fit VQ state in a 16 bit register in > > the general case though, and will have to resort to DMA. > Yes, at least we need in-flight descriptors tracking. > Still working with Eugenio for this feature. > > And if you are > > doing that then please just use the admin command format (does not have > > to be a VQ) and then we can all make peace finally. > >
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