netdev - Re: [PATCH bpf-next v6 2/8] net: Update an existing TCP congestion control algorithm.

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Message-ID: <49fa2455-f591-3062-9780-dadadbf388c8@gmail.com>
Date:   Mon, 13 Mar 2023 09:43:34 -0700
From:   Kui-Feng Lee <sinquersw@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        Kui-Feng Lee <kuifeng@...a.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, kernel-team@...a.com, andrii@...nel.org,
        sdf@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v6 2/8] net: Update an existing TCP congestion
 control algorithm.



On 3/13/23 08:46, Kui-Feng Lee wrote:
> 
> 
> On 3/10/23 08:47, Stephen Hemminger wrote:
>> On Thu, 9 Mar 2023 20:38:07 -0800
>> Kui-Feng Lee <kuifeng@...a.com> wrote:
>>
>>> This feature lets you immediately transition to another congestion
>>> control algorithm or implementation with the same name.  Once a name
>>> is updated, new connections will apply this new algorithm.
>>>
>>> Signed-off-by: Kui-Feng Lee <kuifeng@...a.com>
>>
>> What is the use case and userspace API for this?
>> The congestion control algorithm normally doesn't allow this because
>> algorithm specific variables (current state of connection) may not
>> work with another algorithm.
> 
> Only new connections will apply the new algorithm, while
> existing connections keep using the algorithm applied. It shouldn't
> have the per-connection state/variable issue you mentioned.
> 
> It will be used to upgrade an existing algorithm to a new version.
> The userspace API is used in the 8th patch of this patchset.
> One of examples in the testcase is
> 
>    link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
>    .......
>    err = bpf_link__update_map(link, skel->maps.ca_update_2);
> 
> Calling bpf_link__update_map(...) will register ca_pupdate_2 and
> unregister ca_update_1 with the same name
> in one call.  However, the existing connections that has applied
> ca_update_1 keep using the algorithm except someone call
> setsockopt(TCP_CONGESTION, ...) on them.

FYI!
The thread head of the patchset is
  https://lore.kernel.org/all/20230310043812.3087672-1-kuifeng@meta.com/


> 
> 
> 
>>
>> Seems like you are opening Pandora's box here.
>