Re: [PATCH net-next 1/2] net: More fine-grained support for encapsulated GSO features

On Thu, May 02, 2013 at 09:53:25AM -0700, Jesse Gross wrote:

On Wed, May 1, 2013 at 10:31 PM, Simon Horman [off-list ref] wrote:

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On Wed, May 01, 2013 at 09:53:42PM -0700, Jesse Gross wrote:

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On Wed, May 1, 2013 at 3:57 PM, Simon Horman [off-list ref] wrote:

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On Wed, May 01, 2013 at 11:16:40AM -0700, Jesse Gross wrote:

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On Wed, May 1, 2013 at 12:50 AM, Simon Horman [off-list ref] wrote:

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On Tue, Apr 30, 2013 at 09:19:51AM -0700, Jesse Gross wrote:

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On Mon, Apr 29, 2013 at 8:21 PM, Simon Horman [off-list ref] wrote:

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On Fri, Apr 26, 2013 at 04:03:21PM -0700, Jesse Gross wrote:

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On Thu, Apr 25, 2013 at 12:36 AM, Simon Horman [off-list ref] wrote:

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On Tue, Apr 23, 2013 at 02:00:19PM -0700, Joseph Gasparakis wrote:

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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.

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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.

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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.

Unfortunately my efforts to solicit feedback from others regarding
that have not been successful.

Give me a break, Simon. These are your patches and therefore it is
your responsibility to do the analysis. This has come up over and over
again and I'm not happy about it.

Rather than trying to respond to me as quickly as possible, you need
to slow down, take a step back, and think about the correct direction.
Given that some of these patches have revision numbers in the 20s you
have nothing to complain about as far as receiving help.

In order to assist you in this, I'm going to drop all of your pending
patches from my queue and not respond to anything further from you
until the merge window is open again.

I apologise, the comment I made above was unnecessary.

I accept your criticism in regards to responding to quickly.