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

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Message-ID: <55108bac-9edf-439c-ba54-ee25a1901d6c@kernel.dk>
Date: Wed, 4 Feb 2026 20:48:03 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Pavel Begunkov <asml.silence@...il.com>,
 Bobby Eshleman <bobbyeshleman@...il.com>,
 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,
 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 1/30/26 4:13 AM, Pavel Begunkov wrote:
> On 1/27/26 06:48, Bobby Eshleman wrote:
>> 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).
> 
> Hmm, makes me wonder why not use zcrx instead of reinventing it? It

Was thinking the same throughout most of this later discussion... We
already have an API for this.

-- 
Jens Axboe