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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aA-9aEokobuckLtV@LQ3V64L9R2>
Date: Mon, 28 Apr 2025 10:39:52 -0700
From: Joe Damato <jdamato@...tly.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Martin Karsten <mkarsten@...terloo.ca>,
	Samiullah Khawaja <skhawaja@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	almasrymina@...gle.com, willemb@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v5 0/4] Add support to do threaded napi busy poll

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.