Thinking about Sasha's patches, we can reduce ring usage for virtio net small packets dramatically if we put virtio net header inline with the data. This can be done for free in case guest net stack allocated extra head room for the packet, and I don't see why would this have any downsides. Even though with my recent patches qemu no longer requires header to be the first s/g element, we need a new feature bit to detect this. A trivial qemu patch will be sent separately. We could get rid of an extra s/g for big packets too, but since in practice everyone enables mergeable buffers, I don't see much of a point. Rusty, if you decide to pick this up I'll send a (rather trivial) spec patch shortly afterwards, but holidays are beginning here. Considering how simple the guest patch is, I hope it can make it in 3.7? Also note that patch 1 and 2 are IMO a good idea without patch 3. If you decide to defer patch 3 pls consider 1/2 separately. Before: [root@virtlab203 qemu]# ssh robin ./netperf/bin/netperf -t TCP_RR -H 11.0.0.4 TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.4 (11.0.0.4) port 0 AF_INET : demo Local /Remote Socket Size Request Resp. Elapsed Trans. Send Recv Size Size Time Rate bytes Bytes bytes bytes secs. per sec 16384 87380 1 1 10.00 2992.88 16384 87380 After: [root@virtlab203 qemu]# ssh robin ./netperf/bin/netperf -t TCP_RR -H 11.0.0.4 TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.4 (11.0.0.4) port 0 AF_INET : demo Local /Remote Socket Size Request Resp. Elapsed Trans. Send Recv Size Size Time Rate bytes Bytes bytes bytes secs. per sec 16384 87380 1 1 10.00 3195.57 16384 87380 Michael S. Tsirkin (3): virtio: add API to query ring capacity virtio-net: correct capacity math on ring full virtio-net: put virtio net header inline with data drivers/net/virtio_net.c | 57 +++++++++++++++++++++++++++++++------------- drivers/virtio/virtio_ring.c | 19 +++++++++++++++ include/linux/virtio.h | 2 ++ include/linux/virtio_net.h | 5 +++- 4 files changed, 66 insertions(+), 17 deletions(-) -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
