virtio_net: switch to build_skb for mrg_rxbuf
For small packets data copy was observed to
take up about 15% CPU time. Switch to build_skb
and avoid the copy when using mergeable rx buffers.
As a bonus, medium-size skbs that fit in a page will be
completely linear.
Of course, we now need to lower the lower bound on packet size,
to make sure a sane number of skbs fits in rx socket buffer.
By how much? I don't know yet.
It might also be useful to prefetch the packet buffer since
net stack will likely use it soon.
Lightly tested, in particular, I didn't yet test what this
actually does to performance - sending this out for early
feedback/flames.
TODO: it appears that Linux won't handle correctly the case of first
buffer being very small (or consisting exclusively of virtio header).
This is already the case for current code, so don't bother
testing yet.
TODO: might be unfair to the last packet in a fragment as we include
remaining space if any in its truesize.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
1 file changed
