Re: [PATCH bpf-next] bpf, sockmap: add BPF_F_PERMANENTLY flag for skmsg redirect

[Jakub Sitnicki <jakub@cloudflare.com>]

On Sat, Aug 05, 2023 at 05:42 PM +08, Liu Jian wrote:
> If the sockmap msg redirection function is used only to forward packets
> and no other operation, the execution result of the BPF_SK_MSG_VERDICT
> program is the same each time. In this case, the BPF program only needs to
> be run once. Add BPF_F_PERMANENTLY flag to bpf_msg_redirect_map() and
> bpf_msg_redirect_hash() to implement this ability.
>
> Then we can enable this function in the bpf program as follows:
> bpf_msg_redirect_hash(xx, xx, xx, BPF_F_INGRESS | BPF_F_PERMANENTLY);
>
> Test results using netperf  TCP_STREAM mode:
> for i in 1 64 128 512 1k 2k 32k 64k 100k 500k 1m;then
> netperf -T 1,2 -t TCP_STREAM -H 127.0.0.1 -l 20 -- -m $i -s 100m,100m -S 100m,100m
> done
>
> before:
> 3.84 246.52 496.89 1885.03 3415.29 6375.03 40749.09 48764.40 51611.34 55678.26 55992.78
> after:
> 4.43 279.20 555.82 2080.79 3870.70 7105.44 41836.41 49709.75 51861.56 55211.00 54566.85
>
> Signed-off-by: Liu Jian <liujian56@huawei.com>
> ---

Interesting idea. Potentially opens up the way to redirect without
fallback to backlog thread in the future. If we know the target, then we
can propagate backpressure.

If we go this route, we will need tests. selftests/test_sockmap would
need to be extended, and we will also need some unit tests in test_progs
for corner cases. Corner cases to cover that come to mind: redirect to
self, redirect target socket closed.

I'm out next week, so won't be able to give it a proper review.