Messages in this thread |  | | Date | Wed, 13 Apr 2011 13:57:52 -0400 (EDT) | From | Justin Piszcz <> | Subject | Re: 2.6.38: rt2800usb: high latency (1000ms)? |
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On Wed, 13 Apr 2011, Daniel Halperin wrote:
> Ugh! Couldn't you configure the stupid mailing list filter to only > drop rich text mails that have [PATCH or [RFC or [RFT in the subject, > e.g.? Original mail below. > > (sorry for the resend, Justin and Ivo). > > Dan > > On Wed, Apr 13, 2011 at 9:23 AM, Daniel Halperin > <dhalperi@cs.washington.edu> wrote: >> >> On Wed, Apr 13, 2011 at 9:01 AM, Justin Piszcz <jpiszcz@lucidpixels.com> wrote: >>>> >>>> Can you try disabling powersaving? >>>> iwconfig wlan0 power off >>>> >>> Wow! That was it, now its interactive again. >>> >>> 64 bytes from wireless-host (192.168.1.2): icmp_req=1 ttl=64 time=0.581 ms >>> 64 bytes from wireless-host (192.168.1.2): icmp_req=2 ttl=64 time=0.647 ms >>> >>> Thanks, so its recommend to keep this off then, can that be set as the driver default? >>> >> >> That's a bad idea, what you're seeing is likely completely a red herring. Wi-Fi power saving mode saves energy by putting the RF hardware most of the time. This is a Good Thing. >> Power save is designed to kick in only when the load is very slow; the client's network stack should automatically disable power save during times of high load, e.g., during a download or a VoIP call. You should run some tests to see if this is actually occurring; there may be a bug in the rtl implementation. >> The real problem here is that your ping test has invalid assumptions. One packet/second is not enough load to disable Wi-Fi power save, so you should not see interactive ping times. Again, this is a good thing and something I doubt you want to disable! (Assuming that RTL's implementation isn't fundamentally broken elsewhere) It certainly should NOT be the driver default. >> Try again with sudo ping -i 0.01 -s 1400 (e.g., to ping with large packets every 10 ms); this should probably trigger the logic that automatically disables the power saving mode. Or try pinging while doing a 1 Mbit UDP transfer (e.g., with iperf). >> Dan >
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.
So the fix/workaround, for Debian-based distributions (if you come across this problem):
File: /etc/network/interfaces
-- snip --
# Wireless auto wlan0 iface wlan0 inet dhcp wpa-ssid your-ssid wpa-psk your-private-key post-up /sbin/iwconfig wlan0 power off
-- snip --
Justin.
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