[Bloat] question about ack-filter

[Jonathan Morton]

> On 4 Feb, 2019, at 3:26 am, Evuraan <evuraan at gmail.com> wrote:
> 
> What is ack-filtering? How is it important?  What's the difference
> between ack-filter-aggressive and ack-filter?

Simply put, we sometimes found that downstream throughput was limited by acks on the reverse path, on highly asymmetric links (such as ADSL) loaded in both directions simultaneously.  Because acks are themselves very small, AQM activity by itself wasn't enough to clear the backlog.

Ack-filtering looks for consecutive acks accumulating in a flow queue, and deletes the ones which are not needed, improving throughput and efficiency.  The "aggressive" version deletes more acks, but I think we found it hit too many under certain conditions.

It's harmless to leave it switched on in the non-aggressive mode.  If you're a purist who doesn't like dropping packets, then you can switch it off.

 - Jonathan Morton