On Tue, Sep 29, 2020 at 3:32 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
>
> On Tue, Sep 29, 2020 at 4:00 AM <xiangxia.m.yue@xxxxxxxxx> wrote:
> >
> > From: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
> >
> > Open vSwitch and Linux bridge will disable LRO of the interface
> > when this interface added to them. Now when disable the LRO, the
> > virtio-net csum is disable too. That drops the forwarding performance.
>
> I had focused on the code previously.
>
> The s/w checksum verification cost is significant in a VM with traffic
> to local destinations. A bridge does not verify transport layer
> checksums OTOH?
Hi Willem.
No, think about GRO(In the GRO we don't know packets will be forwarded
to other ports or to local). The call tree as below:
+ 5.41% secondary_startup_64
- 1.22% ret_from_fork
....
net_rx_action
napi_poll
virtnet_poll
virtnet_receive
napi_gro_receive
dev_gro_receive
inet_gro_receive
tcp4_gro_receive
__skb_gro_checksum_complete
skb_checksum
__skb_checksum
csum_partial
do_csum
- 1.13% do_csum
$ brctl show
bridge name bridge id STP enabled interfaces
br0 8000.001122330001 no eth1
eth2
> > Fixes: a02e8964eaf9 ("virtio-net: ethtool configurable LRO")
> > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > Cc: Jason Wang <jasowang@xxxxxxxxxx>
> > Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
> > Signed-off-by: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
> > ---
> > v2:
> > * change the fix-tag
> > ---
> > drivers/net/virtio_net.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 7145c83c6c8c..21b71148c532 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -63,6 +63,11 @@ static const unsigned long guest_offloads[] = {
> > VIRTIO_NET_F_GUEST_CSUM
> > };
> >
> > +#define GUEST_OFFLOAD_LRO_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
> > + (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
> > + (1ULL << VIRTIO_NET_F_GUEST_ECN) | \
> > + (1ULL << VIRTIO_NET_F_GUEST_UFO))
> > +
> > struct virtnet_stat_desc {
> > char desc[ETH_GSTRING_LEN];
> > size_t offset;
> > @@ -2531,7 +2536,8 @@ static int virtnet_set_features(struct net_device *dev,
> > if (features & NETIF_F_LRO)
> > offloads = vi->guest_offloads_capable;
> > else
> > - offloads = 0;
> > + offloads = vi->guest_offloads_capable &
> > + ~GUEST_OFFLOAD_LRO_MASK;
> >
> > err = virtnet_set_guest_offloads(vi, offloads);
> > if (err)
> > --
> > 2.23.0
> >
--
Best regards, Tonghao
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