[Make-wifi-fast] TCP performance regression in mac80211 triggered by the fq code

Michal Kazior michal.kazior at tieto.com
Tue Jul 19 09:10:48 EDT 2016

On 12 July 2016 at 16:02, Dave Taht <dave.taht at gmail.com> wrote:
>>> tcp_limit_output_bytes is?
>> 262144
> I keep hoping to be able to reduce this to something saner like 4096
> one day. It got bumped to 64k based on bad wifi performance once, and
> then to it's current size to make the Xen folk happier.

Not sure if it's possible. You do need this to be at least as big as a
single A-MPDU can get. In extreme 11ac cases it can be pretty big.

I recall a discussion from a long time ago and the tcp limit output
logic was/is coupled with the assumption that tx-completions always
come max 1ms after tx submission. This is rather tricky to *guarantee*
on wifi, especially with firmware blobs, big aggregates, lots of
stations and retries.


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