On 04/21/2011 03:31 PM, Stefan Hajnoczi wrote:
On Thu, Apr 21, 2011 at 9:07 AM, Avi Kivity<avi@xxxxxxxxxx> wrote:
> Note I think in both cases we can make significant improvements:
> - for VFs, steer device interrupts to the cpus which run the vcpus that will
> receive the interrupts eventually (ISTR some work about this, but not sure)
> - for virtio, use a DMA engine to copy data (I think there exists code in
> upstream which does this, but has this been enabled/tuned?)
Which data copy in virtio? Is this a vhost-net specific thing you're
thinking about?
There are several copies.
qemu's virtio-net implementation incurs a copy on tx and on rx when
calling the kernel; in addition there is also an internal copy:
/* copy in packet. ugh */
len = iov_from_buf(sg, elem.in_num,
buf + offset, size - offset);
In principle vhost-net can avoid the tx copy, but I think now we have 1
copy on rx and tx each.
If a host interface is dedicated to backing a vhost-net interface (say
if you have an SR/IOV card) then you can in principle avoid the rx copy
as well.
An alternative to avoiding the copies is to use a dma engine, like I
mentioned.
--
error compiling committee.c: too many arguments to function
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