On 3/10/23 08:47, Stephen Hemminger wrote:
On Thu, 9 Mar 2023 20:38:07 -0800
Kui-Feng Lee <kuifeng@xxxxxxxx> 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@xxxxxxxx>
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.
Seems like you are opening Pandora's box here.
