Re: [gdm-list] Network Latency on timeout

[Brian Cameron <Brian Cameron Sun COM>]

Bill:

It might be worthwhile to write a script that runs the Xserver and kills
it a few times for testing without GDM being involved at all.  This
might help determine if the problem is with the Xserver code or
somewhere else.  Also might be worth testing with other display
managers such as KDM or XDM to see if they have the same problem.

> I have a latency issue, but I doubt it's related directly to gdm.  But
> maybe someone can give me some ideas where to look.
>
> I have a new Thinkpad T60p running Ubuntu Feisty that I often will
> connect to my local LAN, boot it, and close the laptop's lid.  I then
> connect to it via SSH.
>
> After a few minutes the ssh sessions become very slow exhibiting a lot
> of latency when typing.  I have noticed this happens when the gdm
> screen blanks.  If I touch the mouse on the laptop to bring back the
> gdm login screen the latency in my ssh session goes away.
>
> Running top does not show that any process (e.g. screen saver) is
> running using CPU, and the load average is showing 0.01 (or less ;).

Are you saying that GDM is running and that after some time the
screen blanks?  If you aren't running some sort of screensaver
process along with GDM, then this might be some built-in power
management feature.  GDM itself doesn't blank your screen after
any timeout.

If you are logged into a session and running gnome-screensaver,
xscreensaver, or another screen saver, then this program will
lock your session.

> I don't notice any additional network traffic when the latency shows
> up.

If it is power management, then perhaps when the switch happens
some of the computer's services are affected briefly?

> And then if I wait long enough for the screen to turn off (instead of
> just blank) the latency seems to goes away.
>
> I suspect this is an xorg issue, although I only see it when gdm
> blanks.  If I first log in and let the laptop sit until the screen
> blanks I don't see the latency.  That may be related to how GNOME
> times out, though.

There might be some odd interaction between power management and Xorg,
but I don't think Xorg has any sort of power management or screen
saving logic built in directly.

> I'd like to test dpms (to see if that's really what triggers
> the latency) by forcing the monitor blank and off.
>
> If I log in with gdm on the laptop then via an ssh session I can run
> DISPLAY=:0.0 xset -q.  But, how can I access xset over ssh when the
> laptop is sitting at a gdm login?  I tried su'ing to both root and to
> user "gdm" which is what gdmgreeter is running as.

You need the Xauth key that the gdm GUI programs are running as.  The
root user should be able to get these from /var/lib/gdm.  Or you could
configure GDM to run in unprotected "xauth +" mode.  I wouldn't advise
running on the network this way, but for running a few tests off
the network, it should be okay.

> I've posted a few other places without any luck, so at this point I'm
> just looking for debugging suggestions.

Hope this helps.

Brian