[Bloat] [bbr-dev] Aggregating without bloating - hard times for tcp and wifi

[Toke Høiland-Jørgensen]

Neal Cardwell via Bloat <bloat at lists.bufferbloat.net> writes:

> On Tue, Nov 22, 2022 at 2:43 PM 'Bob McMahon' via BBR Development <
> bbr-dev at googlegroups.com> wrote:
>
>> Thanks for sharing this. Curious about how the xTSQ value can be set? Can
>> it be done with sysctl?
>>
>> *We continue our analysis by using the ms-version of TSQ patch, which
>> enables the tune of the TSQ size allowing each TCP variant to enqueue more
>> than 1 ms of data at the current TCP rate. In particular, we allow to
>> enqueue the equivalent of x ms of data, naming each test xTSQ, with x being
>> an integer value. It is important to notice that this patch has been
>> included in the Linux kernel mainline, and each Wi-Fi driver can now set
>> the desired xTSQ value**.*
>>
>
> I believe they are setting the xTSQ value using the sk_pacing_shift field,
> which was added here:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3a9b76fd0db9f0d426533f96a68a62a58753a51e
>
> AFAIK the intent is only for drivers to set that, and there's no sysctl for
> that, but of course you could add a sysctl for testing if you wanted.
> :-)

Yup, indeed this is what mac80211 fiddles with:
https://elixir.bootlin.com/linux/latest/source/net/mac80211/main.c#L739
https://elixir.bootlin.com/linux/latest/source/net/mac80211/tx.c#L4156

AFAICT, no in-tree drivers override the value set by mac80211.

I believe the tests in that paper were conducted with this series
applied:
https://lore.kernel.org/all/20180105113256.14835-1-natale.patriciello@gmail.com/

-Toke