On 10 Jul 2026, at 17:29, Ilya Maximets wrote:
> As a general rule, code that requires ALLOW_EXPERIMENTAL_API is not
> allowed on the main branch.
>
> The exemption was granted to the tunnel offload implementation because
> it was a large piece of code that is hard to maintain separately and
> there was a hope that it will become stable in a relatively short
> amount of time. That was 5 years ago, so clearly that didn't work out.
>
> In the current code, even the parts that could be generic are gated
> by the ALLOW_EXPERIMENTAL_API macro. The reason is the noticeable
> performance impact packet metadata restoration API has on every packet
> even when the traffic is not offloaded. There was an attempt to make
> it faster by providing a dynamic mbuf flag, but checking dynamic flags
> still causes performance impact due to a series of indirect calls into
> DPDK per packet.
>
> We don't have test coverage for this code on main, we don't even build
> it in CI on main (and we shouldn't), and there is no much hope for it
> to become performant enough to become stable within a reasonable time
> frame.
>
> So, it's time to remove this code from main. It can live in the
> dpdk-latest branch where we have at least some compilation tests for
> the experimental API. And if someday it becomes stable, we can add
> it back to main. Though the code would likely need to be re-reviewed
> as it at least has some style issues.
>
> With this code removed, there are no more offload providers that
> implements post processing and can return EOPNOTSUPP on a per-device
> basis. However, calling into a separate translation unit, getting
> RCU-protected offload provider and checking if the method exists is
> still expensive if done per packet. Simple vhost-to-vhost forwarding
> test with offload enabled (but not supported, obviously) shows 1-1.5%
> performance degradation. So, the early check of the
> 'post_process_api_supported' before calling into dpif_offload module
> is still needed.
>
> Signed-off-by: Ilya Maximets <[email protected]>
Thanks for getting the v2 out! Changes look good to me.
Acked-by: Eelco Chaudron <[email protected]>
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