Re: [PATCH 7/9] rt2x00: Fix rt2800 USB TX Path DMA issue

[Johannes Stezenbach <js@sig21.net>]

On Mon, Nov 15, 2010 at 01:45:24AM -0800, Walter Goldens wrote:
> 
> These patches appear to have finally brought some life in to the rt307x chips
> in terms of stability and usability. There are no more duplicate (very few)
> or lost packets and overall, the driver is improved immensely, however the
> latency is increased compared to the STA driver. Pinging my gateway with STA
> yields about 2-3ms average, whereas the rt2800usb is about 8-9ms. The
> throughput is also about 20% less.

I'm runnung rt2800usb (RT3070) in AP mode, and when pinging
from the client I get:

[12631.727724] phy0 -> rt2x00usb_watchdog_tx_status: Warning - TX queue 2 status timed out, invoke forced tx handler
[12632.727451] phy0 -> rt2x00usb_watchdog_tx_status: Warning - TX queue 2 status timed out, invoke forced tx handler
[12638.728027] phy0 -> rt2x00usb_watchdog_tx_status: Warning - TX queue 2 status timed out, invoke forced tx handler
[12674.732633] phy0 -> rt2x00usb_watchdog_tx_status: Warning - TX queue 0 status timed out, invoke forced tx handler
[12676.732855] phy0 -> rt2x00usb_watchdog_tx_status: Warning - TX queue 0 status timed out, invoke forced tx handler
[12679.733581] phy0 -> rt2x00usb_watchdog_tx_status: Warning - TX queue 0 status timed out, invoke forced tx handler
[12779.745991] phy0 -> rt2x00usb_watchdog_tx_status: Warning - TX queue 0 status timed out, invoke forced tx handler
etc.

I wonder why it is using TX queue 2?  Isn't this QID_AC_VI, i.e.
it should only be used when some programs uses setsockopt SO_PRIORITY
to request QoS for video data?


Lokking through the code, in rt2x00mac_tx():
	enum data_queue_qid qid = skb_get_queue_mapping(skb);
is passed to rt2x00queue_get_queue() which uses
enum data_queue_qid has 2 == QID_AC_VI, but net/core/dev.c dev_pick_tx()
calls skb_set_queue_mapping() with 2 == BE
(from ieee802_1d_to_ac, return by ieee80211_netdev_select_queue())

Maybe I'm just confused?


Queue stats after some flood pinging:

# cat /sys/kernel/debug/ieee80211/phy0/rt2800usb/queue/queue 
qid     count   limit   length  index   dma done        done
14      199365  128     128     69      69      69
0       785     64      1       18      18      17
1       0       64      0       0       0       0
2       196406  64      0       54      54      54
3       0       64      0       0       0       0
16      0       8       0       0       0       0


Johannes