Re: [Qemu-devel] [net-next RFC PATCH 0/7] multiqueue support for tun/tap

[Sridhar Samudrala]

On Fri, 2011-08-12 at 09:54 +0800, Jason Wang wrote:
> As multi-queue nics were commonly used for high-end servers,
> current single queue based tap can not satisfy the
> requirement of scaling guest network performance as the
> numbers of vcpus increase. So the following series
> implements multiple queue support in tun/tap.
> 
> In order to take advantages of this, a multi-queue capable
> driver and qemu were also needed. I just rebase the latest
> version of Krishna's multi-queue virtio-net driver into this
> series to simplify the test. And for multiqueue supported
> qemu, you can refer the patches I post in
> http://www.spinics.net/lists/kvm/msg52808.html. Vhost is
> also a must to achieve high performance and its code could
> be used for multi-queue without modification. Alternatively,
> this series can be also used for Krishna's M:N
> implementation of multiqueue but I didn't test it.
> 
> The idea is simple: each socket were abstracted as a queue
> for tun/tap, and userspace may open as many files as
> required and then attach them to the devices. In order to
> keep the ABI compatibility, device creation were still
> finished in TUNSETIFF, and two new ioctls TUNATTACHQUEUE and
> TUNDETACHQUEUE were added for user to manipulate the numbers
> of queues for the tun/tap.

Is it possible to have tap create these queues automatically when
TUNSETIFF is called instead of having userspace to do the new
ioctls. I am just wondering if it is possible to get multi-queue
to be enabled without any changes to qemu. I guess the number of queues
could be based on the number of vhost threads/guest virtio-net queues.

Also, is it possible to enable multi-queue on the host alone without
any guest virtio-net changes?

Have you done any multiple TCP_RR/UDP_RR testing with small packet
sizes? 256byte request/response with 50-100 instances? 

> 
> I've done some basic performance testing of multi queue
> tap. For tun, I just test it through vpnc.
> 
> Notes:
> - Test shows improvement when receving packets from
> local/external host to guest, and send big packet from guest
> to local/external host.
> - Current multiqueue based virtio-net/tap introduce a
> regression of send small packet (512 byte) from guest to
> local/external host. I suspect it's the issue of queue
> selection in both guest driver and tap. Would continue to
> investigate.
> - I would post the perforamnce numbers as a reply of this
> mail.
> 
> TODO:
> - solve the issue of packet transmission of small packets.
> - addressing the comments of virtio-net driver
> - performance tunning
> 
> Please review and comment it, Thanks.
> 
> ---
> 
> Jason Wang (5):
>       tuntap: move socket/sock related structures to tun_file
>       tuntap: categorize ioctl
>       tuntap: introduce multiqueue related flags
>       tuntap: multiqueue support
>       tuntap: add ioctls to attach or detach a file form tap device
> 
> Krishna Kumar (2):
>       Change virtqueue structure
>       virtio-net changes
> 
> 
>  drivers/net/tun.c           |  738 
> ++++++++++++++++++++++++++-----------------
>  drivers/net/virtio_net.c    |  578 ++++++++++++++++++++++++----------
>  drivers/virtio/virtio_pci.c |   10 -
>  include/linux/if_tun.h      |    5 
>  include/linux/virtio.h      |    1 
>  include/linux/virtio_net.h  |    3 
>  6 files changed, 867 insertions(+), 468 deletions(-)
>