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

From: Daniel Halperin
Date: Wed Apr 13 2011 - 12:26:54 EST

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).


On Wed, Apr 13, 2011 at 9:23 AM, Daniel Halperin
<dhalperi@xxxxxxxxxxxxxxxxx> wrote:
> On Wed, Apr 13, 2011 at 9:01 AM, Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:
>>> Can you try disabling powersaving?
>>> iwconfig wlan0 power off
>> Wow! That was it, now its interactive again.
>> 64 bytes from wireless-host ( icmp_req=1 ttl=64 time=0.581 ms
>> 64 bytes from wireless-host ( 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
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at