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

    > On Wed, 13 Apr 2011, Daniel Halperin wrote:
    >
    >> On Wed, Apr 13, 2011 at 10:57 AM, Justin Piszcz
    >> <jpiszcz@lucidpixels.com> wrote:
    >>> Hi,
    >>>
    >>> When powersave is enabled, it is very jumpy, I've used satellite comms
    >>> before
    >>> and (~600ms-1200ms was more smooth) as it did not jump around as
    >>> much. The
    >>> application is just a standalone desktop with minimal activity for the
    >>> majority
    >>> of the time, maybe thats why..
    >>>
    >>> With powersave disabled, I now see 0% packet loss (802.11n) and low
    >>> ping
    >>> times, this looks like the proper solution for the wireless USB
    >>> device I
    >>> am using. By the way, is it possible/are there wireless USB devices
    >>> out
    >>> there
    >>> that support wake on wireless lan (WOWL?
    >>>
    >>> Your ping command with power off:
    >>> 1408 bytes from server (192.168.1.2): icmp_req=539 ttl=64 time=1.07 ms
    >>> 1408 bytes from server (192.168.1.2): icmp_req=540 ttl=64 time=1.31 ms
    >>> 1408 bytes from server (192.168.1.2): icmp_req=541 ttl=64 time=1.07 ms
    >>> 1408 bytes from server (192.168.1.2): icmp_req=542 ttl=64 time=1.26 ms
    >>>
    >>> Your ping command with power on:
    >>> 1408 bytes from server (192.168.1.2): icmp_req=649 ttl=64 time=1.80 ms
    >>> 1408 bytes from server (192.168.1.2): icmp_req=650 ttl=64 time=1.85 ms
    >>> 1408 bytes from server (192.168.1.2): icmp_req=651 ttl=64 time=2.86 ms
    >>> 1408 bytes from server (192.168.1.2): icmp_req=652 ttl=64 time=1.46 ms
    >>>
    >>> You are correct, if there is a lot of traffic, its good, but if the
    >>> system
    >>> is relatively idle and all that's going on is an SSH session, there is
    >>> horrible
    >>> latency.
    >>
    >> Gotcha. I might still look around in the network stack and/or driver
    >> and see what the time constants are. For instance:
    >>
    >> (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.
    >
    >
    >>
    >> (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.

    Yes, it's terrible. I have the same problems with ping and ssh with
    latest GIT
    linux on my ARM platform and two different USB Wi-Fi adapters based on
    RT3070 chipset ("D-Link DWA-125" and "Qcom LR802UKN3").

    >
    >>
    >> 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
    >
    >
    > 100+0 records in
    > 100+0 records out
    > 104857600 bytes (105 MB) copied, 23.2803 s, 4.5 MB/s
    >
    > Justin.

    Best regards!
    --
    Igor Plyatov


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