Re: infinite transmit buffering issue in 2.6.32 mac80211

[Kalle Valo <kalle.valo@iki.fi>]

Lennert Buytenhek <buytenh@wantstofly.org> writes:

> Hi!

Hello,

> Since "mac80211: remove master netdev", mac80211 no longer propagates
> TX queue full status (ieee80211_stop_queue et al) up.  While the
> underlying hardware's TX queue is stopped, mac80211 buffers frames
> internally (in ieee80211_tx), but there's no upper limit on the number
> of frames it will buffer, leading to badness when there is heavy TX
> traffic on the wireless interface:

We have noticed very strange throughput degration both with wl1251 and
wl1271. With 2.6.28 both drivers were able to achieve 10 Mbit/s
throughput over TCP, but with 2.6.32 (and almost the same drivers) we
get less than 4 Mbit/s. Because we see it both with wl1251 and wl1271,
we are starting to suspect that it's a problem in mac80211.

We haven't started analysing this yet, but I'm hoping someone from our
team to start it soon. I have no idea if our problem is related to the
problem Lennert reports or not, but we will definitely try Johannes'
patch and see if it helps.

-- 
Kalle Valo