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Subjectno HLT at GDM?
OK, I'm not a subscriber (although I check kernel-traffic pretty
regular), so please email responses to ekl@wans.net. I'm asking here
cause this could be a kernel issue ... and well ... you guys are the
only ones I can think of that know linux better than I do. But
something WEIRD is happening

Here's the situation. The computer is overclocked from 450Mhz to 500Mhz
(ok, flog me latter, I know its a "bad thing" - but it seems to be
noticeably faster especially booting, and the problem happens when I
keep it at 450Mhz as well). Its an AMD K6-2, rated at 450Mhz, its the
2.4V core version (I heard there are 2.2V core versions as well, and I
run 2.4V at 450Mhz, and 2.5 at 500Mhz). This is the same internal core
as the K6-3 (design change for 400Mhz and up processors) but without the
large second level cache of the K6-3 (but the slower motherboard cache
is 2MB on my motherboard - if that is relevant, its also a VIA
chipset). I have the system cooled (with a peltier and lots of fans,
again - kill me later) and normally runs around 12-14 degrees C at idle
or doing non-intensive work - playing an mp3 while playing on the
internet for example - I realize thats pretty intensive for windblows,
but not for Linux. The system will go to 40-45 degrees C running OpenGL
screen-savers. Kernel compile keeps CPU about the same as case temp.
While playing Q3 Arena (with voodoo banshee acceleration) I can hit 50
C. Condensation and possible harm from temperature fluctuations are
prolly more of a concern than heat (AMD rates the processor up to 65
C). Temp changes are very fast cooling almost a degree a second once
the system goes idle (measured with lm_sensors at a serial terminal -
I can watch it cool down).

Now, here's the problem. If I log out of X to just the GDM screen, the
system will heat up to 45 C, as if I was thrashing it with an OpenGL
screen-saver, but unlike running an app like xscreensaver, I'm not
seeing any system load. Running "top" shows the system is 99.8% idle.
No processes are accruing<sp?> any significant amount of total processor
time usage (except X), and nothing is in a run state (other than top).
The system is 99.8% idle and yet something is making the processor heat
up. If I log in to X, gnome comes up and the system will cool down to
the low to mid teens. I know the kernel makes HLT instructions at idle
and this will keep the processor VERY cool, but it doesn't seem to do it
when I log out of gnome to the GDM login screen. Being logged in at the
terminal doesn't change anything, and I can't test virtual consoles
cause my monitor doesn't (yet) sync to text modes (might use frame
buffer console, but vmware says it won't work with it). Something is
stopping the kernel from issuing HLT instructions it would seem, but GDM
should be just sitting and waiting for user events like any other X app
- and according to top, it is - not stuck in a busy polling-loop.

Sorry for the long post, but I thought the details might help. If
anyone has any clue why I have to log in to keep the CPU cool, I'd love
to hear it. I'm guessing a bug somewhere, and if anyone can tell me
where to look for it, I'll be glad to find it and squash it.

Thanks,
Evan Langlois
ekl@wans.net



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