linux-kernel - Re: [PATCH net-next v10 0/5] net: devmem: improve cpu cost of RX token management

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Message-ID: <CAKB00G3p9_VUTEW_KQvS1JAd+Ju_pjrU5r-v_p+K8Y=vH__mTQ@mail.gmail.com>
Date: Mon, 26 Jan 2026 22:48:33 -0800
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>, Mina Almasry <almasrymina@...gle.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	Neal Cardwell <ncardwell@...gle.com>, David Ahern <dsahern@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Jonathan Corbet <corbet@....net>, Andrew Lunn <andrew+netdev@...n.ch>, Shuah Khan <shuah@...nel.org>, 
	Donald Hunter <donald.hunter@...il.com>, Stanislav Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	asml.silence@...il.com, matttbe@...nel.org, skhawaja@...gle.com, 
	Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v10 0/5] net: devmem: improve cpu cost of RX
 token management

On Mon, Jan 26, 2026 at 10:00 PM Stanislav Fomichev
<stfomichev@...il.com> wrote:
>
> On 01/26, Jakub Kicinski wrote:
> > On Mon, 26 Jan 2026 10:45:22 -0800 Bobby Eshleman wrote:
> > > I'm onboard with improving what we have since it helps all of us
> > > currently using this API, though I'm not opposed to discussing a
> > > redesign in another thread/RFC. I do see the attraction to locating the
> > > core logic in one place and possibly reducing some complexity around
> > > socket/binding relationships.
> > >
> > > FWIW regarding nl, I do see it supports rtnl lock-free operations via
> > > '62256f98f244 rtnetlink: add RTNL_FLAG_DOIT_UNLOCKED' and routing was
> > > recently made lockless with that. I don't see / know of any fast path
> > > precedent. I'm aware there are some things I'm not sure about being
> > > relevant performance-wise, like hitting skb alloc an additional time
> > > every release batch. I'd want to do some minimal latency comparisons
> > > between that path and sockopt before diving head-first.
> >
> > FTR I'm not really pushing Netlink specifically, it may work it
> > may not. Perhaps some other ioctl-y thing exists. Just in general
> > setsockopt() on a specific socket feels increasingly awkward for
> > buffer flow. Maybe y'all disagree.
> >
> > I thought I'd clarify since I may be seen as "Mr Netlink Everywhere" :)
>
> From my side, if we do a completely new uapi, my preference would be on
> an af_xdp like mapped rings (presumably on a netlink socket?) to completely
> avoid the user-kernel copies.

I second liking that approach. No put_cmsg() and or token alloc overhead (both
jump up in my profiling).