On Wed, May 1, 2013 at 3:57 PM, Simon Horman <ho...@verge.net.au> wrote: > On Wed, May 01, 2013 at 11:16:40AM -0700, Jesse Gross wrote: >> On Wed, May 1, 2013 at 12:50 AM, Simon Horman <ho...@verge.net.au> wrote: >> > On Tue, Apr 30, 2013 at 09:19:51AM -0700, Jesse Gross wrote: >> >> On Mon, Apr 29, 2013 at 8:21 PM, Simon Horman <ho...@verge.net.au> wrote: >> >> > On Fri, Apr 26, 2013 at 04:03:21PM -0700, Jesse Gross wrote: >> >> >> On Thu, Apr 25, 2013 at 12:36 AM, Simon Horman <ho...@verge.net.au> >> >> >> wrote: >> >> >> > On Tue, Apr 23, 2013 at 02:00:19PM -0700, Joseph Gasparakis wrote: >> >> >> >> Any particular reason to introduce skb->encapsulation_features >> >> >> >> instead of >> >> >> >> using the existing skb->encapsulation? Also I don't see it used in >> >> >> >> your >> >> >> >> second patch either. >> >> >> > >> >> >> > My reasoning is that skb->encapsulation seems to alter the behaviour >> >> >> > of >> >> >> > many different locations and I'm not sure that any of them, other >> >> >> > than the >> >> >> > one in dev_hard_start_xmit() make sense for MPLS. >> >> >> >> >> >> The problem is the meaning of skb->encapsulation isn't really defined >> >> >> clearly and I'm certain that the current implementation is not going >> >> >> to work in the future. Depending on your perspective, vlans, MPLS, >> >> >> tunnels, etc. can all be considered forms of encapsulation but clearly >> >> >> there are many NICs that have different capabilities across those. I >> >> >> believe the intention here was really to describe L3 tunnels as >> >> >> encapsulation, in which case MPLS really shouldn't be using this >> >> >> mechanism at all. >> >> >> >> >> >> Now there is some overlap, especially today since most currently >> >> >> shipping silicon wasn't designed to support tunnels and so is using >> >> >> some form of offset based offloads. In that case, all forms of >> >> >> encapsulation are pretty similar. However, in the future that won't be >> >> >> the case as support for specific protocols is implemented for higher >> >> >> performance and richer support. When that happens, not only will MPLS >> >> >> and tunnels have different capabilities but various forms tunnels >> >> >> might as well. >> >> > >> >> > Wouldn't be possible to describe those differences using, >> >> > dev->hw_enc_features? I assumed that was its purpose. >> >> >> >> If there truly are differences between the offload capabilities of >> >> MPLS and L3 tunnels then no, it's not possible, because it's a single >> >> field. It's certainly not a valid assumption that a NIC that can do >> >> TSO over GRE can also do it over MPLS. >> >> >> >> However, it's unlikely that there are truly significant differences >> >> between various encapsulation formats on a per-feature basis. I think >> >> what we need to do is separate out the ability to understand the >> >> headers from the capabilities so you have two fields: header (none, >> >> VLAN, QinQ, MPLS, VXLAN, GRE, etc.) and feature (checksum, SG, TSO, >> >> etc.) rather than the product of each. Otherwise, we end up with a ton >> >> of different combinations. >> > >> > I'm not quite sure that I follow. >> > >> > Is your idea to replace skb->encapsulation (a single bit) with >> > a field that corresponds to the outer-most (encapsulation) header in use >> > and has bits for none, VLAN, QinQ, MPLS, VXLAN, GRE, etc...? >> >> No, I'm talking about netdev features. You can already tell the >> encapsulation type of a packet by looking at the EtherType. > > Now I am completely confused about what are the two fields that you > refer to in your previous email.
I have always been referring to the netdev features for various protocol types. This is because considering MPLS as a form of encapsulation for the purpose of offloads buckets too many protocols into the same set and NICs will have varying features for those. Trying to avoid this by having a bit for offloadable encapsulations is just going to be very confusing and not very future proof. > In regards to looking ath the ethernet type: > > One of the tricky parts of MPLS is that the packet itself does not contain > the ethernet type or any other way of knowing the type of the inner-packet. > Information that is needed for GSO. I'm aware of that. However, you were referring to the type of encapsulation. It is easy to determine that a packet is MPLS. > My proposal to get around this is to leave skb->protocol as the > original, in the case we are interested in non-MPLS, ethernet type. At the very least, this is not consistent with how it is currently handled (for example, with VLANs) and seems difficult to do properly. However, I have not seen any further analysis since the last time that we discussed this. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
