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


    On Wed, 13 Apr 2011, Daniel Halperin wrote:

    > On Wed, Apr 13, 2011 at 1:13 PM, Justin Piszcz <jpiszcz@lucidpixels.com> 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
    >
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