Re: [RFC PATCH v8 00/16] Provide a zero-copy method on KVMvirtio-net.

From: Shirley Ma
Date: Thu Jul 29 2010 - 18:31:33 EST

Hello Xiaohui,

On Thu, 2010-07-29 at 19:14 +0800, wrote:
> The idea is simple, just to pin the guest VM user space and then
> let host NIC driver has the chance to directly DMA to it.
> The patches are based on vhost-net backend driver. We add a device
> which provides proto_ops as sendmsg/recvmsg to vhost-net to
> send/recv directly to/from the NIC driver. KVM guest who use the
> vhost-net backend may bind any ethX interface in the host side to
> get copyless data transfer thru guest virtio-net frontend.

Since vhost-net already supports macvtap/tun backends, do you think
whether it's better to implement zero copy in macvtap/tun than inducing
a new media passthrough device here?

> Our goal is to improve the bandwidth and reduce the CPU usage.
> Exact performance data will be provided later.

I did some vhost performance measurement over 10Gb ixgbe, and found that
in order to get consistent BW results, netperf/netserver, qemu, vhost
threads smp affinities are required.

Looking forward to these results for small message size comparison. For
large message size 10Gb ixgbe BW already reached by doing vhost smp
affinity w/i offloading support, we will see how much CPU utilization it
can be reduced.

Please provide latency results as well. I did some experimental on
macvtap zero copy sendmsg, what I have found that get_user_pages latency
pretty high.


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