netdev - Re: [PATCH net-next v3 3/7] net: ethtool: add support for configuring tcp-data-split-thresh

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: <CAHS8izNZhr6=82Piv74V1HuVT1X+OEEyxUXs-VU46KJt3Fu5mA@mail.gmail.com>
Date: Thu, 3 Oct 2024 18:47:01 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Taehee Yoo <ap420073@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	edumazet@...gle.com, netdev@...r.kernel.org, linux-doc@...r.kernel.org, 
	donald.hunter@...il.com, corbet@....net, michael.chan@...adcom.com, 
	kory.maincent@...tlin.com, andrew@...n.ch, maxime.chevallier@...tlin.com, 
	danieller@...dia.com, hengqi@...ux.alibaba.com, ecree.xilinx@...il.com, 
	przemyslaw.kitszel@...el.com, hkallweit1@...il.com, ahmed.zaki@...el.com, 
	paul.greenwalt@...el.com, rrameshbabu@...dia.com, idosch@...dia.com, 
	asml.silence@...il.com, kaiyuanz@...gle.com, willemb@...gle.com, 
	aleksander.lobakin@...el.com, dw@...idwei.uk, sridhar.samudrala@...el.com, 
	bcreeley@....com
Subject: Re: [PATCH net-next v3 3/7] net: ethtool: add support for configuring tcp-data-split-thresh

On Thu, Oct 3, 2024 at 12:33 PM Taehee Yoo <ap420073@...il.com> wrote:
>
> On Fri, Oct 4, 2024 at 3:25 AM Mina Almasry <almasrymina@...gle.com> wrote:
> >
> > On Thu, Oct 3, 2024 at 9:07 AM Taehee Yoo <ap420073@...il.com> wrote:
> > >
> > > The tcp-data-split-thresh option configures the threshold value of
> > > the tcp-data-split.
> > > If a received packet size is larger than this threshold value, a packet
> > > will be split into header and payload.
> >
> > Why do you need this? devmem TCP will always not work with unsplit
> > packets. Seems like you always want to set thresh to 0 to support
> > something like devmem TCP.
> >
> > Why would the user ever want to configure this? I can't think of a
> > scenario where the user wouldn't want packets under X bytes to be
> > unsplit.
>
> I totally understand what you mean,
> Yes, tcp-data-split is zerocopy friendly option but as far as I know,
> this option is not only for the zerocopy usecase.
> So, If users enable tcp-data-split, they would assume threshold is 0.
> But there are already NICs that have been supporting tcp-data-split
> enabled by default.
> bnxt_en's default value is 256bytes.
> If we just assume the tcp-data-split-threshold to 0 for all cases,
> it would change the default behavior of bnxt_en driver(maybe other drivers too)
> for the not zerocopy case.
> Jakub pointed out the generic case, not only for zerocopy usecase
> in the v1 and I agree with that opinion.
> https://lore.kernel.org/netdev/20240906183844.2e8226f3@kernel.org/

I see, thanks. The ability to tune the threshold to save some pcie
bandwidth is interesting. Not sure how much it would matter in
practice. I guess if you're receiving _lots_ of small packets then it
could be critical.

Sounds good then, please consider adding Jakub's reasoning for why
tuning this could be valuable to the commit message for future
userspace readers that wonder why to set this.

-- 
Thanks,
Mina