On Fri, May 13, 2022 at 10:03:13AM +0200, Felix Fietkau wrote:

On 13.05.22 09:49, Pablo Neira Ayuso wrote:

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Hi,

On Tue, May 10, 2022 at 10:27:39PM +0200, Felix Fietkau wrote:

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In many cases, it's not easily possible for user space to know, which
devices properly support hardware offload.

Then, it is a matter of extending the netlink interface to expose this
feature? Probably add a FLOW_BLOCK_PROBE or similar which allow to
consult if this feature is available?

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Even if a device supports hardware flow offload, it is not
guaranteed that it will actually be able to handle the flows for
which hardware offload is requested.

When might this happen?

I think there are many possible reasons: The flow might be using features
not supported by the offload driver. Maybe it doesn't have any space left in
the offload table. I'm sure there are many other possible reasons it could
fail.

This fallback to software flowtable path for partial scenarios already
exists.

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Ignoring errors on the FLOW_BLOCK_BIND makes it a lot easier to set up
configurations that use hardware offload where possible and gracefully
fall back to software offload for everything else.

I understand this might be useful from userspace perspective, because
forcing the user to re-try is silly.

However, on the other hand, the user should have some way to know from
the control plane that the feature (hardware offload) that they
request is not available for their setup.

In my opinion, most users of this API probably don't care and just want to
have offload on a best effort basis.

OK, but if the setup does not support hardware offload at all, why
should the control plane accept this? I think user should know in
first place that no one single flow is going to be offloaded to
hardware.

Assuming that is the case, wouldn't it be better if we simply have
an API that indicates, which flowtable members hardware offload was
actually enabled for?

What are you proposing?

I think it would be good to expose through netlink interface what the
device can actually do according to the existing supported flowtable
software datapath features.