Re: [Qemu-devel] [PATCH] net: QEMU_NET_PACKET_FLAG_MORE introduced

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Dec 09, 2013 at 11:20:29AM +0100, Vincenzo Maffione wrote:
> Hello,
>    I've done some netperf TCP_STREAM and TCP_RR virtio-net tests, using the
> same configuration.
> Here are the results
> 
> ########## netperf TCP_STREAM ###########
>         NO BATCHING         BATCHING
> 1          5.5 Gbps         3.8 Gbps
> 2          5.4 Gbps         5.5 Gbps
> 3          5.2 Gbps         5.2 Gbps
> 4          5.1 Gbps         5.0 Gbps
> 10         5.4 Gbps         5.2 Gbps
> 20         5.4 Gbps         5.4 Gbps
> 
> 
> ############ netperf TCP_RR #############
>         NO BATCHING         BATCHING
> 1         13.0 Ktts         12.8 Ktts
> 2         23.8 Ktts         23.0 Ktts
> 3         34.0 Ktts         32.5 Ktts
> 4         44.5 Ktts         41.0 Ktts
> 10        97.0 Ktts         93.0 Ktts
> 15       122.0 Ktts        120.0 Ktts
> 20       125.0 Ktts        128.0 Ktts
> 25       128.0 Ktts        130.0 Ktts
> 
> 
> There is some negative effects introduced by batching.
> Also consider that
>    - Since TAP backend doesn't use the new flag, this patch doesn't change the
> performance when the TAP backend is used.
>    - I've not submitted yet the patch for virtio_net_header support, and
> therefore the TCP_STREAM performance with NETMAP backend is now not
>      comparable to the performance with TAP backend, because we are limited to
> 1.5KB packets.
> 
> Cheers,
>   Vincenzo

Ah, so no GSO/UFO/checksum offload then?
In that case maybe it's a good idea to start with supporting
that in your backend. This does batching within the guest so
extra host side batching with all the tradeoffs it involves
might not be necessary.

Guest network stack behaviour with and without offloads is
different to such a degree that it's not clear optimizing
one is not pessimizing the other.

-- 
MST