Re: [Bloat] Comcast & L4S

[Jonathan Morton <chromatix99@gmail.com>]

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> On 1 Feb, 2025, at 8:05 pm, Sebastian Moeller <moeller0@gmx.de> wrote:
> 
>> about as tight as you can reasonably make it while still accommodating typical levels of link-level jitter.  
> 
> Not sure, in a LAN with proper back pressure I would guess lower than 5ms to be achievable. This does not need to go crazy low, so 1 ms would likely do well, with an interval of 10ms... or if 5 ms is truly a sweet spot, maybe decouple interval and target so these can be configured independently (in spite of the theory that recommends target to be 5-10% of interval).

Actually, the 5ms target is already too tight for efficient TCP operation on typical Internet paths - unless there is significant statistical multiplexing on the bottleneck link, which is rarely the case in a domestic context.  Short RTTs on a LAN allow for achieving full throughput with the queue held this small, but remember that the concept of "LAN" also includes WiFi links whose median latency is orders of magnitude greater than that of switched Ethernet.  That's why I don't want to encourage going below 5ms too much.

DelTiC actually reverts to the 25ms queue target that has historically been typical for AQMs targeting conventional TCP.  It adopts 5ms only for SCE marking.  This configuration works very well in testing so far:



As for CPU efficiency, that is indeed something to keep in mind.  The scheduling logic in Cake got very complex in the end, and there are undoubtedly ways to avoid that with a fresh design.

 - Jonathan Morton


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