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

[Jens Axboe <axboe@kernel.dk>]

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@gmail.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