Messages in this thread | | | Date | Thu, 14 Apr 2011 09:17:08 +0400 | From | Igor Plyatov <> | Subject | Re: 2.6.38: rt2800usb: high latency (1000ms)? |
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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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