On Fri, 7 Dec 2012, Ben Hutchings wrote:
> On Fri, 2012-12-07 at 08:45 -0800, Alexander Duyck wrote:
> > On 12/07/2012 02:07 AM, Ben Hutchings wrote:
> > > On Thu, 2012-12-06 at 17:56 -0800, Joseph Gasparakis wrote:
> > >> This patch adds support in the kernel for offloading in the NIC Tx and Rx
> > >> checksumming for encapsulated packets (such as VXLAN and IP GRE).
> > > [...]
> > >> --- a/include/linux/netdevice.h
> > >> +++ b/include/linux/netdevice.h
> > >> @@ -1063,6 +1063,8 @@ struct net_device {
> > >> netdev_features_t wanted_features;
> > >> /* mask of features inheritable by VLAN devices */
> > >> netdev_features_t vlan_features;
> > >> + /* mask of features inherited by encapsulating devices */
> > >> + netdev_features_t hw_enc_features;
> > > [...]
> > >
> > > How will the networking core know *which* encapsulations this applies
> > > to? I notice that your implementation in ixgbe does not set
> > > NETIF_F_HW_CSUM here, so presumably the hardware will parse headers to
> > > find which ranges should be checksummed and it won't cover the next
> > > encapsulation protocol that comes along.
> > >
> > > Ben.
> > >
> >
> > Actually the offload is generic to any encapsulation that does not
> > compute a checksum on the inner headers. So as long as you can treat
> > the outer headers as one giant L2 header you can pretty much ignore what
> > is in there as long as the inner network and transport header values are
> > set. There are a number of tunnels that fall into that category since
> > most just use IP as the L2 and the L3 usually doesn't contain any checksum.
>
> Yes, that should work, but it requires that the driver/hardware uses the
> header offsets from the skb rather than parsing the packet. This is not
> currently required for devices with the NETIF_F_IP_CSUM and
> NETIF_F_IPV6_CSUM features.
>
> Please do state explicitly which feature flags are valid in
> hw_enc_features, any changes in semantics, and in particular in what
> cases the driver/hardware is supposed to use header offsets from the skb
> vs parsing the packet.
>
> Ben.
>
So the idea here is that the driver will use the headers for checksumming
if the skb->encapsulation bit is on. The bit should be set in the protocol
driver.
To answer the second comment, the flags that we use in this series of
patches is NETIF_F_IP_CSUM, NETIF_F_IPV6_CSUM and NETIF_F_SG. These are
the bits that we propose will be used for checksumming of encapsulation.
As per a previous comment in v2, the hw_enc_features field should be used
also in the future when NICs have more encap offloads, so one could
indicate these features there from the driver.
Furthermore, I submitted a patch for Rx checksumming, where NETIF_F_RXCSUM
is used, again in conjunction with skb->encapsulation flag. As I mention
in my logs, the driver is expected to set the ip_summed to UNNECESSARY and
turn the skb->encapsulation on, to indicate that the inner headers are
already HW checksummed.
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