Network latency when gdm login times out

Bill Moseley moseley at hank.org
Thu Aug 2 17:33:53 UTC 2007


I have a Thinkpad T60p running Feisty.  I often connect it to my local
LAN, boot the machine and close the lid.  I then ssh into the machine.

I have been experiencing quite a bit of latency in my ssh sessions,
and after testing cabling and my switch I realized the latency happens
when the gdm login window times out and the screen goes blank.

By latency I mean typing becomes difficult as there is a quite a bit
of delay between hitting a key and for it to be echoed.

    - no screen saver is running, just X going to a blank screen

    - only happens when gdm login screen blanks, not when I'm logged
      into GNOME desktop and it goes into screen-saver mode.

    - load average is 0.00 -- nothing is eating CPU

    - strace on gdbgreeter, gdm, and /usr/X11R6/bin/X show no activity

    - ifconfig doesn't show a lot of traffic in RX/TX packets.
      Interface is not saturated.

    - if I wait long enough it seems like the latency clears up.

That last point is curious.  IIRC, the laptop first just blanks the
screen but leaves the back-light turned on.  Then later the back-light
turns off.  I'm starting to suspect the delay is only when the screen
is blanked.

To test that I want to force different dpms settings.


When I log in via the gdm to my GNOME desktop I can then ssh into the
laptop and run:

    DISPLAY=:0.0 xset -q

to get information about the display.  But, how can I do something
similar when the laptop is sitting at the gdm login?  gdm runs as
root, and gdmgreeter runs as user gdm.  I've su'ed to both users and
tried running the above xset command.

Anyone know how to run xset for the gdm login?

The reason I want access to xset is to force suspend and see if that
triggers the latency.




-- 
Bill Moseley
moseley at hank.org





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