On 08/19/2015 08:20 PM, Eric Dumazet wrote:

On Wed, 2015-08-19 at 17:00 +0000, Grumbach, Emmanuel wrote:

quoted

On 08/19/2015 07:08 PM, Eric Dumazet wrote:

quoted

On Wed, 2015-08-19 at 15:07 +0000, Grumbach, Emmanuel wrote:

quoted

I'll look at it.
I was almost starting to implement that but then I thought with another
(good?) reason to use LSO. LSO gives me the guarantee that the packet is
directed to one peer, which might not be the case with xmit_more since
we have one Qdisc for several clients in case we are in AP mode.
Building an A-MSDU for several clients is not possible, at least not for
several client in the L2 (different MAC addresses).
LSO avoids this problem completely.

Then, simply calling skb_gso_segment() from the driver might be enough,
and less work for you.

This would even support TSO on IPv6

Well... I did take care of IPv6.

net/core/tso.c does not yet handle IPv6

Yeah - I can see that now.
I can teach him - that's not a big deal. The bigger problem is that
net/core/tso.c doesn't do what I really need: it does only a small
portion. Since I need to add one frag to several skbs, I need to
refcount the frags' page. net/core/tso.c hides the page from me.

I can try to use tso_build_hdr but it will copy the entire header where
I need only SNAP / IP / TCP (and not 802.11).
I am getting the feeling that net/core/tso.c is close to what I need,
but not close enough to be usable without making changes that would make
the implementation too complicated and changing net/core/tso.c in a way
that would be much less readable for other users.
I know that our device is quite "unique" in the sense that most other
vendors do all the header twiddling in hardware. We unfortunately don't.
The A-MSDU's format is also somewhat unusual:

<802.11 HDR>
	<ETH><SNAP><IP><TCP><PAYLOAD><PAD (variable length)
	<ETH><SNAP><IP><TCP><PAYLOAD><PAD (variable length)
	<ETH><SNAP><IP><TCP><PAYLOAD><PAD (variable length)
	etc...

So I feel that making net/core/tso.c more complicated just because of
our craziness seems an overkill to me.
I'll try a bit harder to see how I can use net/core/tso.c, but I have to
say I am pessimistic.
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