Re: [PATCH 3.3] rt2x00: fix random stalls

Hi,

I'm very sorry about the size of my previous mail. I hope that it was not too trouble.

/ Martin

On 03/06/2012 06:43 PM, Martin Hundebøll wrote:

Hi,

On 03/05/2012 05:48 PM, Stanislaw Gruszka wrote:

quoted

Is possible that we stop queue and then do not wake up it again,
especially when packets are transmitted fast. That can be easily
reproduced with modified tx queue entry_num to some small value e.g. 16.

If mac80211 already hold local->queue_stop_reason_lock, then we can wait
on that lock in both rt2x00queue_pause_queue() and
rt2x00queue_unpause_queue(). After drooping ->queue_stop_reason_lock
is possible that __ieee80211_wake_queue() will be performed before
__ieee80211_stop_queue(), hence we stop queue and newer wake up it
again.

To prevent stalls serialize pause/unpause by queue->tx_lock.

I've been having CPU load issues with rt2800usb/Ralink RT2870, when doing simultaneous TX/RX between to nodes in an adhoc network. While transfering UDP packets in one direction with iperf[1], I get ~23Mbit/s and kworker is utilizing <10% of the CPU (OMAP4 1GHz dualcore or/and Pentium M 1.70GHz) on both ends. When doing bidirectional tests with iperf[2], one kworker thread jumps too 100% and throughput drops.

By using two iperf clients to do bidirectional TCP transfers, I got ~6Mbit/s in both directions, so I suspected some queueing issues and thus applied this patch, but no change. I've tried to do some tracing[3], but this is quite new to me, so please instruct me, if you need more info.

Kind regards,
Martin Hundebøll

[1]
 iperf unidirectional cmd and output:
# iperf -c10.10.10.56 -ub50M
Server Report:
0.0-10.0 sec  27.5 MBytes  22.9 Mbits/sec   1.639 ms    0/19602 (0%)

[2]
 iperf bidirectional cmd and output:
# iperf -c10.10.10.56 -udb8M
Sent 2501 datagrams
[  3]  0.0-11.0 sec  1.26 MBytes   963 Kbits/sec  22.437 ms  943/ 1840 (51%)
Server Report:
[  4]  0.0-10.9 sec  2.11 MBytes  1.62 Mbits/sec  309.803 ms  993/ 2500 (40%)

[3]
out.txt has a trace from 10.10.10.55 while running iperf as in [2] and the following commands:
$ echo workqueue:workqueue_queue_work > /sys/kernel/debug/tracing/set_event
$ cat /sys/kernel/debug/tracing/trace_pipe > out.txt