This reverts commit 484a54c2e5. The CoDel
parameter change essentially disables CoDel on slow stations, with some
questionable assumptions, as Dave pointed out in [0]. Quoting from
there:
But here are my pithy comments as to why this part of mac80211 is so
wrong...
static void sta_update_codel_params(struct sta_info *sta, u32 thr)
{
- if (thr && thr < STA_SLOW_THRESHOLD * sta->local->num_sta) {
1) sta->local->num_sta is the number of associated, rather than
active, stations. "Active" stations in the last 50ms or so, might have
been a better thing to use, but as most people have far more than that
associated, we end up with really lousy codel parameters, all the
time. Mistake numero uno!
2) The STA_SLOW_THRESHOLD was completely arbitrary in 2016.
- sta->cparams.target = MS2TIME(50);
This, by itself, was probably not too bad. 30ms might have been
better, at the time, when we were battling powersave etc, but 20ms was
enough, really, to cover most scenarios, even where we had low rate
2Ghz multicast to cope with. Even then, codel has a hard time finding
any sane drop rate at all, with a target this high.
- sta->cparams.interval = MS2TIME(300);
But this was horrible, a total mistake, that is leading to codel being
completely ineffective in almost any scenario on clients or APS.
100ms, even 80ms, here, would be vastly better than this insanity. I'm
seeing 5+seconds of delay accumulated in a bunch of otherwise happily
fq-ing APs....
100ms of observed jitter during a flow is enough. Certainly (in 2016)
there were interactions with powersave that I did not understand, and
still don't, but if you are transmitting in the first place, powersave
shouldn't be a problemmmm.....
- sta->cparams.ecn = false;
At the time we were pretty nervous about ecn, I'm kind of sanguine
about it now, and reliably indicating ecn seems better than turning it
off for any reason.
[...]
In production, on p2p wireless, I've had 8ms and 80ms for target and
interval for years now, and it works great.
I think Dave's arguments above are basically sound on the face of it,
and various experimentation with tighter CoDel parameters in the OpenWrt
community have show promising results[1]. So I don't think there's any
reason to keep this parameter fiddling; hence this revert.
[0] https://lore.kernel.org/linux-wireless/CAA93jw6NJ2cmLmMauz0xAgC2MGbBq6n0ZiZzAdkK0u4b+O2yXg@mail.gmail.com/
[1] https://forum.openwrt.org/t/reducing-multiplexing-latencies-still-further-in-wifi/133605/130
Suggested-By: Dave Taht <dave.taht@gmail.com>
In-memory-of: Dave Taht <dave.taht@gmail.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20250403183930.197716-1-toke@toke.dk
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
4876376988