Re: 2.6.38: rt2800usb: high latency (1000ms)?

From: Justin Piszcz
Date: Wed Apr 13 2011 - 16:36:14 EST

On Wed, 13 Apr 2011, Daniel Halperin wrote:

On Wed, Apr 13, 2011 at 1:13 PM, Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:
(1) What is the AP's beacon period and DTIM? Typical values are 100
TUs for beacons (102.4 ms) and 2 for DTIM (2 beacons per power-save
wakeup) which should imply a mean of 100 and max of 200 ms delay even
on pings.

I am using a WNDR3700 with default settings in terms of beacons/etc.  No
issues with any device (laptop, computer, etc (in windows)), I have two
wireless USB adapters (bought two) and in Windows, no problems, I don't
it is the WNDR3700.  As far as linux/wpa-supplicant, using default settings.

Not enough info. What does "iw dev wlan1 scan dump" (it might not be
wlan1 for you) say for "beacon interval"?

# iw dev wlan0 scan dump

BSS (hidden) (on wlan0) -- associated
TSF: 103430650682 usec (1d, 04:43:50)
freq: 2417
beacon interval: 100
capability: ESS Privacy ShortPreamble ShortSlotTime (0x0431)
signal: -59.00 dBm
last seen: 1345742 ms ago
SSID: (hidden)
Supported rates: 1.0* 2.0* 5.5* 11.0* 6.0 9.0 12.0 18.0
DS Parameter set: channel 2
RSN: * Version: 1
* Group cipher: TKIP
* Pairwise ciphers: CCMP TKIP
* Authentication suites: PSK
* Capabilities: (0x0000)
WPA: * Version: 1
* Group cipher: TKIP
* Pairwise ciphers: CCMP TKIP
* Authentication suites: PSK
ERP: <no flags>
Extended supported rates: 24.0 36.0 48.0 54.0
WMM: * Parameter version 1
* u-APSD
* BE: CW 15-1023, AIFSN 3
* BK: CW 15-1023, AIFSN 7
* VI: CW 7-15, AIFSN 2, TXOP 3008 usec
* VO: acm CW 3-7, AIFSN 2, TXOP 1504 usec
HT capabilities:
Capabilities: 0x11ce
SM Power Save disabled
RX STBC 1-stream
Max AMSDU length: 7935 bytes
Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
Minimum RX AMPDU time spacing: 1/2 usec (0x02)
HT RX MCS rate indexes supported: 0-15
HT TX MCS rate indexes are undefined
WPS: * Version: 1.0
* Manufacturer: Netgear, Inc.
* Model: WNDR3700
* Device name: (hidden)
* Config methods: Ethernet, Label, PBC

Does anyone know how to get the DTIM period out of iw?

(2) How long does the client wait after waking up to go back to sleep?
It should be at least a few seconds. For ssh, then, you should see
something like a 100-200 ms delay for the first key and then nothing
at all unless you stop typing for a bit.

It lags with each word I type, it is terrible.  If I run something like
dmesg or ps auxww, the entire session freezes for 5-10 seconds before it
comes back.

Sorry; I meant what is the software stack configured to do? Do some
looking around.

I'm SSHing over a Wi-Fi link that uses power save right this second,
and have for years. It's not generally an issue, I suspect something
worse is going on.

Maybe the wireless usb adapters do not function well in Linux with power

I bought them awhile ago, they had the highest reviews, and in Windows,
they did do 10-15MiB/s, in Linux, I see ~4.6MiB/s (but that was with power
save on) about the same, 4.5MiB/s.

Yeah, these might indicate a fairly sizable problem in the Linux drivers IMO.