[Qemu-devel] [Bug 1546445] Re: support vhost user without specifying vhostforce

[Louis Bouchard]

** Also affects: qemu (Ubuntu Wily)
   Importance: Undecided
       Status: New

** Also affects: qemu (Ubuntu Vivid)
   Importance: Undecided
       Status: New

** Also affects: qemu (Ubuntu Trusty)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1546445

Title:
  support vhost user without specifying vhostforce

Status in QEMU:
  In Progress
Status in qemu package in Ubuntu:
  New
Status in qemu source package in Trusty:
  New
Status in qemu source package in Vivid:
  New
Status in qemu source package in Wily:
  New

Bug description:
  [Impact]

   * vhost-user falls back to virtio-net which causes performance lose
  without specifying the vhostforce option. But it should be the default
  behavior for vhost-user, since guests using PMD doesn't support msi-x.

  [Test Case]

    create a vhost-user virtio backend without specifying the vhostforce 
option, i.e. -netdev 
type=vhost-user,id=mynet1,chardev=<char_dev_for_the_controll_channel>
    start the VM
    vhost-user is not enabled

  [Regression Potential]

   * none

  vhost user nic doesn't support non msi guests(like pxe stage) by default.
  Vhost user nic can't fall back to qemu like normal vhost net nic does. So we 
should
  enable it for non msi guests.

  The problem has been fix in qemu upstream  -
  
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=24f938a682d934b133863eb421aac33592f7a09e.
  And the patch needs to be backported to 1:2.2+dfsg-5expubuntu9.8 .

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