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Subject: Re: [virtio-comment] Re: [PATCH v3 6/8] admin: Add theory of operation for write recording commands
On Fri, Nov 17, 2023 at 01:03:03PM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin <mst@redhat.com> > > Sent: Friday, November 17, 2023 6:02 PM > > > > On Fri, Nov 17, 2023 at 12:11:15PM +0000, Parav Pandit wrote: > > > > > > > > > > From: Michael S. Tsirkin <mst@redhat.com> > > > > Sent: Friday, November 17, 2023 5:35 PM > > > > To: Parav Pandit <parav@nvidia.com> > > > > > > > > On Fri, Nov 17, 2023 at 11:45:20AM +0000, Parav Pandit wrote: > > > > > > > > > > > From: Michael S. Tsirkin <mst@redhat.com> > > > > > > Sent: Friday, November 17, 2023 5:04 PM > > > > > > > > > > > > On Fri, Nov 17, 2023 at 11:05:16AM +0000, Parav Pandit wrote: > > > > > > > > > > > > > > > > > > > > > > From: Michael S. Tsirkin <mst@redhat.com> > > > > > > > > Sent: Friday, November 17, 2023 4:30 PM > > > > > > > > > > > > > > > > On Fri, Nov 17, 2023 at 10:03:47AM +0000, Parav Pandit wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com> > > > > > > > > > > Sent: Friday, November 17, 2023 3:30 PM > > > > > > > > > > > > > > > > > > > > On 11/16/2023 7:59 PM, Michael S. Tsirkin wrote: > > > > > > > > > > > On Thu, Nov 16, 2023 at 06:28:07PM +0800, Zhu, Lingshan > > wrote: > > > > > > > > > > >> > > > > > > > > > > >> On 11/16/2023 1:51 PM, Michael S. Tsirkin wrote: > > > > > > > > > > >>> On Thu, Nov 16, 2023 at 05:29:54AM +0000, Parav Pandit > > wrote: > > > > > > > > > > >>>> We should expose a limit of the device in the > > > > > > > > > > >>>> proposed > > > > > > > > > > WRITE_RECORD_CAP_QUERY command, that how much range it > > > > > > > > > > can > > > > > > track. > > > > > > > > > > >>>> So that future provisioning framework can use it. > > > > > > > > > > >>>> > > > > > > > > > > >>>> I will cover this in v5 early next week. > > > > > > > > > > >>> I do worry about how this can even work though. If > > > > > > > > > > >>> you want a generic device you do not get to dictate > > > > > > > > > > >>> how much memory VM > > > > > > has. > > > > > > > > > > >>> > > > > > > > > > > >>> Aren't we talking bit per page? With 1TByte of > > > > > > > > > > >>> memory to track > > > > > > > > > > >>> -> 256Gbit -> 32Gbit -> 8Gbyte per VF? > > > > > > > > > > >>> > > > > > > > > > > >>> And you happily say "we'll address this in the future" > > > > > > > > > > >>> while at the same time fighting tooth and nail > > > > > > > > > > >>> against adding single bit status registers because scalability? > > > > > > > > > > >>> > > > > > > > > > > >>> > > > > > > > > > > >>> I have a feeling doing this completely theoretical > > > > > > > > > > >>> like this is > > > > > > problematic. > > > > > > > > > > >>> Maybe you have it all laid out neatly in your head > > > > > > > > > > >>> but I suspect not all of TC can picture it clearly > > > > > > > > > > >>> enough based just on spec > > > > > > text. > > > > > > > > > > >>> > > > > > > > > > > >>> We do sometimes ask for POC implementation in linux > > > > > > > > > > >>> / qemu to demonstrate how things work before merging > > code. > > > > > > > > > > >>> We skipped this for admin things so far but I think > > > > > > > > > > >>> it's a good idea to start doing it here. > > > > > > > > > > >>> > > > > > > > > > > >>> What makes me pause a bit before saying please do a > > > > > > > > > > >>> PoC is all the opposition that seems to exist to > > > > > > > > > > >>> even using admin commands in the 1st place. I think > > > > > > > > > > >>> once we finally stop arguing about whether to use > > > > > > > > > > >>> admin commands at all then a PoC will be needed > > > > > > > > before merging. > > > > > > > > > > >> We have POR productions that implemented the approach > > > > > > > > > > >> in my > > > > > > series. > > > > > > > > > > >> They are multiple generations of productions in > > > > > > > > > > >> market and running in customers data centers for years. > > > > > > > > > > >> > > > > > > > > > > >> Back to 2019 when we start working on vDPA, we have > > > > > > > > > > >> sent some samples of production(e.g., Cascade > > > > > > > > > > >> Glacier) and the datasheet, you can find live > > > > > > > > > > >> migration facilities there, includes suspend, vq state and other > > features. > > > > > > > > > > >> > > > > > > > > > > >> And there is an reference in DPDK live migration, I > > > > > > > > > > >> have provided this page > > > > > > > > > > >> before: > > > > > > > > > > >> https://doc.dpdk.org/guides-21.11/vdpadevs/ifc.html, > > > > > > > > > > >> it has been working for long long time. > > > > > > > > > > >> > > > > > > > > > > >> So if we let the facts speak, if we want to see if > > > > > > > > > > >> the proposal is proven to work, I would > > > > > > > > > > >> say: They are POR for years, customers already > > > > > > > > > > >> deployed them for > > > > > > years. > > > > > > > > > > > And I guess what you are trying to say is that this > > > > > > > > > > > patchset we are reviewing here should be help to the > > > > > > > > > > > same standard and there should be a PoC? Sounds reasonable. > > > > > > > > > > Yes and the in-marketing productions are POR, the series > > > > > > > > > > just improves the design, for example, our series also > > > > > > > > > > use registers to track vq state, but improvements than > > > > > > > > > > CG or BSC. So I think they are proven > > > > > > > > to work. > > > > > > > > > > > > > > > > > > If you prefer to go the route of POR and production and > > > > > > > > > proven documents > > > > > > > > etc, there is ton of it of multiple types of products I can > > > > > > > > dump here with open- source code and documentation and more. > > > > > > > > > Let me know what you would like to see. > > > > > > > > > > > > > > > > > > Michael has requested some performance comparisons, not > > > > > > > > > all are ready to > > > > > > > > share yet. > > > > > > > > > Some are present that I will share in coming weeks. > > > > > > > > > > > > > > > > > > And all the vdpa dpdk you published does not have basic > > > > > > > > > CVQ support when I > > > > > > > > last looked at it. > > > > > > > > > Do you know when was it added? > > > > > > > > > > > > > > > > It's good enough for PoC I think, CVQ or not. > > > > > > > > The problem with CVQ generally, is that VDPA wants to shadow > > > > > > > > CVQ it at all times because it wants to decode and cache the > > > > > > > > content. But this problem has nothing to do with dirty > > > > > > > > tracking even though it also > > > > > > mentions "shadow": > > > > > > > > if device can report it's state then there's no need to shadow CVQ. > > > > > > > > > > > > > > For the performance numbers with the pre-copy and device > > > > > > > context of > > > > > > patches posted 1 to 5, the downtime reduction of the VM is 3.71x > > > > > > with active traffic on 8 RQs at 100Gbps port speed. > > > > > > > > > > > > Sounds good can you please post a bit more detail? > > > > > > which configs are you comparing what was the result on each of them. > > > > > > > > > > Common config: 8+8 tx and rx queues. > > > > > Port speed: 100Gbps > > > > > QEMU 8.1 > > > > > Libvirt 7.0 > > > > > GVM: Centos 7.4 > > > > > Device: virtio VF hardware device > > > > > > > > > > Config_1: virtio suspend/resume similar to what Lingshan has, > > > > > largely vdpa stack > > > > > Config_2: Device context method of admin commands > > > > > > > > OK that sounds good. The weird thing here is that you measure "downtime". > > > > What exactly do you mean here? > > > > I am guessing it's the time to retrieve on source and re-program > > > > device state on destination? And this is 3.71x out of how long? > > > Yes. Downtime is the time during which the VM is not responding or receiving > > packets, which involves reprogramming the device. > > > 3.71x is relative time for this discussion. > > > > Oh interesting. So VM state movement including reprogramming the CPU is > > dominated by reprogramming this single NIC, by a factor of almost 4? > Yes. Could you post some numbers too then? I want to know whether that would imply that VM boot is slowed down significantly too. If yes that's another motivation for pci transport 2.0. -- MST
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