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

[Neal Cardwell <ncardwell@google.com>]

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On Tue, Nov 22, 2022 at 2:43 PM 'Bob McMahon' via BBR Development <
bbr-dev@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. :-)

cheers,
neal




> Another thing that could be interesting is the WiFi aggregation stop
> reasons, e.g. how many times agg stopped per hitting the max mpdu per ampdu
> vs the software fifo going empty (i.e. no more packets available to the
> driver from the TCP stack) per that TXOP.
>
> Finally, many (most?) APs are forwarding and feeding packets at at the
> hardware level so not sure that the linux stack matters as much for an AP
> based analysis, particularly when considering multi user transmissions,
> i.e. multiple WiFi clients are active and sharing TXOPs.
>
> Bob
> On Mon, Nov 21, 2022 at 10:04 PM Dave Taht <dave.taht@gmail.com> wrote:
>
>> This paper came out last month. Good work, really exhaustive look at
>> two chipsets, multiple congestion controls and the interactions with
>> TSQ, with
>> lots and lots of flent.
>>
>> https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9772053
>>
>> as for wifi6... don't make me start talking about wifi6... but some of
>> these tests look like a good baseline to start comparing the ath11k,
>> mt79, etc..
>>
>> Paper kind of misses the negative impact of AQL in the ath10k (and
>> most likely also the mt76 and mt79 chips)
>>
>> --
>> This song goes out to all the folk that thought Stadia would work:
>>
>> https://www.linkedin.com/posts/dtaht_the-mushroom-song-activity-6981366665607352320-FXtz
>> Dave Täht CEO, TekLibre, LLC
>>
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>>
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