[Make-wifi-fast] tx queue stuck for many minutes

[Toke Høiland-Jørgensen]

Joshua Zhao <swzhao at gmail.com> writes:

> That makes sense. I guess missing TX completion could be potential suspect
> and I'll check on that.
>
> On the other hand, why I ask about back-pressure is because when the
> problem happens the UDP TX socket shows as stuck and doesn't take any new
> packets.
>
> ~# netstat -tulnp
>
> Active Internet connections (only servers)
>
> Proto Recv-Q Send-Q Local Address           Foreign Address         State
>     PID/Program name
>
> udp        0  22400 0.0.0.0:48439           0.0.0.0:*
>     2407/audiod-xxxxx
>
> Basically the "Send-Q" number stays as a very high number for long time (I
> didn't save what the exact number is when the problem happens) in the above
> example, so that the sendto() function simply fails.
> This is why I wondered about back-pressure being applied.  Otherwise
> shouldn't UDP socket keeps sending and packets would be dropped by the
> queue scheduler?

I would expect so; mac80211 only ever returns NETDEV_TX_OK from its
netif_start_xmit() function. Guess the socket layer can stall out for
some reason, or something?

-Toke