Re: [Patch bpf-next v3 4/5] skmsg: use skb ext instead of TCP_SKB_CB

Lorenz Bauer wrote:

On Mon, 15 Feb 2021 at 19:20, John Fastabend [off-list ref] wrote:

quoted

Cong Wang wrote:

quoted

From: Cong Wang <redacted>

Currently TCP_SKB_CB() is hard-coded in skmsg code, it certainly
does not work for any other non-TCP protocols. We can move them to
skb ext instead of playing with skb cb, which is harder to make
correct.

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Reviewed-by: Lorenz Bauer <redacted>
Signed-off-by: Cong Wang <redacted>
---

I'm not seeing the advantage of doing this at the moment. We can
continue to use cb[] here, which is simpler IMO and use the ext
if needed for the other use cases. This is adding a per packet
alloc cost that we don't have at the moment as I understand it.

John, do you have a benchmark we can look at? Right now we're arguing
in the abstract.

Sure, but looks like Cong found some spare fields in sk_buff so
that looks much nicer.

I'll mess aound a bit with our benchmarks and see where we can
publish them. It would be good to have some repeatable tests
here folks can use.

Thanks,
John