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

[Justin Piszcz]

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
> > think
> > 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
                        HT20/HT40
                        SM Power Save disabled
                        RX HT40 SGI
                        TX STBC
                        RX STBC 1-stream
                        Max AMSDU length: 7935 bytes
                        DSSS/CCK HT40
                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
> > save
> > on.
> >
> > 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.
> > http://www.amazon.com/Medialink-Wireless-Adapter-802-11n-Compatible/dp/B002RM08RE
>
> Yeah, these might indicate a fairly sizable problem in the Linux drivers IMO.
>
> Dan