Re: [PATCH net-next v5 0/4] Add support to do threaded napi busy poll

[Joe Damato <jdamato@fastly.com>]

On Mon, Apr 28, 2025 at 12:52:11PM -0400, Willem de Bruijn wrote:
> Martin Karsten wrote:
> > On 2025-04-24 16:02, Samiullah Khawaja wrote:

> Ack on documentation of the pros/cons.

In my mind this includes documenting CPU usage which I know is
considered as "non-goal" of this series. It can be a "non-goal" but
it is still very relevant to the conversation and documentation.

> There is also a functional argument for this feature. It brings
> parity with userspace network stacks like DPDK and Google's SNAP [1].
> These also run packet (and L4+) network processing on dedicated cores,
> and by default do so in polling mode. An XDP plane currently lacks
> this well understood configuration. This brings it closer to parity.

It would be good if this could also be included in the cover letter,
I think, possibly with example use cases.

> Users of such advanced environments can be expected to be well
> familiar with the cost of polling. The cost/benefit can be debated
> and benchmarked for individual applications. But there clearly are
> active uses for polling, so I think it should be an operating system
> facility.

You mention users of advanced environments, but I think it's
important to consider the average user who is not necessarily a
kernel programmer.

Will that user understand that not all apps support this? Or will
they think that they can simply run a few YNL commands burning CPUs at
100% for apps that don't even support this thinking they are making
their networking faster?

I think providing a mechanism to burn CPU cores at 100% CPU by
enabling threaded busy poll has serious consequences on power
consumption, cooling requirements, and, errr, earth. I don't think
it's a decision to be taken lightly.