NetworkingTodo

This page should cover all networking related activity in KVM, currently most info is related to virtio-net.

TODO: add bugzilla entry links.

=== projects in progress. contributions are still very wellcome!

• vhost-net scalability tuning: threading for many VMs

     Plan: switch to workqueue shared by many VMs
     www.mail-archive.com/kvm@vger.kernel.org/msg69868.html
     Developer: Shirley Ma?, MST
     Testing: netperf guest to guest

• multiqueue support in macvtap

      multiqueue is only supported for tun.
      Add support for macvtap.
      Developer: Jason Wang

• enable multiqueue by default

      Multiqueue causes regression in some workloads, thus
      it is off by default. Detect and enable/disable
      automatically so we can make it on by default
      Developer: Jason Wang

• guest programmable mac/vlan filtering with macvtap

       Developer: Dragos Tatulea?, Amos Kong
       Status: GuestProgrammableMacVlanFiltering

• bridge without promisc mode in NIC

 given hardware support, teach bridge
 to program mac/vlan filtering in NIC
 Helps performance and security on noisy LANs
 http://comments.gmane.org/gmane.linux.network/266546
 Developer: Vlad Yasevich

• reduce networking latency:

 allow handling short packets from softirq or VCPU context
 Plan:
   We are going through the scheduler 3 times
   (could be up to 5 if softirqd is involved)
   Consider RX: host irq -> io thread -> VCPU thread ->
   guest irq -> guest thread.
   This adds a lot of latency.
   We can cut it by some 1.5x if we do a bit of work
   either in the VCPU or softirq context.
 Testing: netperf TCP RR - should be improved drastically
          netperf TCP STREAM guest to host - no regression
 Developer: MST

• Flexible buffers: put virtio header inline with packet data

 https://patchwork.kernel.org/patch/1540471/
 Developer: MST

• device failover to allow migration with assigned devices

 https://fedoraproject.org/wiki/Features/Virt_Device_Failover
 Developer: Gal Hammer, Cole Robinson, Laine Stump, MST

• Reuse vringh code for better maintainability

 Developer: Rusty Russell

• Improve stats, make them more helpful for per analysis

 Developer: Sriram Narasimhan

• Bug: e1000 & rtl8139: Change macaddr in guest, but not update to qemu (info network)

 Developer: Amos Kong

projects that are not started yet - no owner

• netdev polling for virtio.

 See http://lkml.indiana.edu/hypermail/linux/kernel/1303.0/00553.html

• receive side zero copy

 The ideal is a NIC with accelerated RFS support,
 So we can feed the virtio rx buffers into the correct NIC queue.
 Depends on non promisc NIC support in bridge.

• IPoIB infiniband bridging

 Plan: implement macvtap for ipoib and virtio-ipoib

• RDMA bridging

• use kvm eventfd support for injecting level interrupts,

 enable vhost by default for level interrupts

• DMA emgine (IOAT) use in tun

• virtio API extension: improve small packet/large buffer performance:

 support "reposting" buffers for mergeable buffers,
 support pool for indirect buffers

=== vague ideas: path to implementation not clear

• ring redesign:

     find a way to test raw ring performance 
     fix cacheline bounces 
     reduce interrupts

• support more queues

    We limit TUN to 8 queues 

• irq/numa affinity:

    networking goes much faster with irq pinning:
    both with and without numa.
    what can be done to make the non-pinned setup go faster?

• reduce conflict with VCPU thread

   if VCPU and networking run on same CPU,
   they conflict resulting in bad performance.
   Fix that, push vhost thread out to another CPU
   more aggressively.

• rx mac filtering in tun

       the need for this is still not understood as we have filtering in bridge
       we have a small table of addresses, need to make it larger
       if we only need filtering for unicast (multicast is handled by IMP filtering)

• vlan filtering in tun

       the need for this is still not understood as we have filtering in bridge

• vlan filtering in bridge

       IGMP snooping in bridge should take vlans into account

testing projects

Keeping networking stable is highest priority.

• Run weekly test on upstream HEAD covering test matrix with autotest

non-virtio-net devices

• e1000: stabilize

test matrix

DOA test matrix (all combinations should work):

       vhost: test both on and off, obviously
       test: hotplug/unplug, vlan/mac filtering, netperf,
            file copy both ways: scp, NFS, NTFS
       guests: linux: release and debug kernels, windows
       conditions: plain run, run while under migration,
               vhost on/off migration
       networking setup: simple, qos with cgroups
       host configuration: host-guest, external-guest