[Bug 1556306] Re: vhost-user: qemu stops processing packets under high load of traffic

[Serge Hallyn]

** Description changed:

+ [SRU Justification]
+ Impact: qemu stops processing traffic
+ Test case: see below (stress test using udp traffic generator)
+ Fix: cherrypick of upstream patch to fix this problem.
+ 
  Description of problem:
  - qemu socket becomes full, causing qemu to send incomplete
  SET_VRING_CALL messages to vhost-user backend (without proper fd set in
  ancillary data).
  - after some time, some interrupts are lost, causing the VM to stop
  transmitting packets.
  
  How reproducible:
  Run a stress tests of a vhost-user interface using an UDP
  traffic generator. Traffic generator (IXIA) was connected to 2 physical ports that are in turn connected to 2 virtio ports through a linux bridge, VM
  (running linux) doing routing to forward packets between the 2 virtio ports.
  When traffic reaches high pps rates of small packets,
  
  Actual results:
  - VM stop transmitting packets
  
  Expected results:
  - VM should never stop transmitting packets
  
  Additional info:
  We do propose a fix at:
-   http://lists.nongnu.org/archive/html/qemu-devel/2015-12/msg00652.html
+   http://lists.nongnu.org/archive/html/qemu-devel/2015-12/msg00652.html

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https://bugs.launchpad.net/bugs/1556306

Title:
   vhost-user: qemu stops processing packets under high load of traffic

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