I have just noticed that inserting a usb key in my computer, a
MSI K8T Neo (MS-6702) MB, using the Via K8T800 chipset, with
AMD 64 3700+ CPU, causes the reported CPU temperature,
via lm_sensors, to increase by about 4 degrees C over the space
of a minute of so. The CPU load does not change in the
gkrellm display while this temperature increase is under way.
I am running Debian Sarge with kernel 2.6.15.2 compiled from
source from kernel.org.
I did an install of W2K SP4 on a 6 GB scratch IDE drive and
found that the same temperature change occurs under MSW,
suggesting that it is not OS dependent. I suspect it is
in the MB firmware.
I then connected a watt meter to the computer and found that
the idle power usage under Linux was about 106 watts. Inserting
a usb key in one of the built in USB ports causes the power
usage to jump by about 30 watts, to a total of about 136. Of course
it does not take long for the CPU temp to rise by about 4 degrees C.
However, the CPU load shows no change. The power usage and the
temperature rise remain when the usb key is removed. Only a reboot
will reset the system. Removing the usb-storage related modules
might also cut the power. I have not tried that yet. Need to recompile
every USB item as a module to do that.
If I load the system with a large-scale simulation of
flow in a river, we have a peak power usage of about 157 watts.
The CPU temperature increases by about 4-5 degrees C
from the level it reaches with only the USB key inserted.
Finally, I added a PCI card with 5 USB ports to the system, and inserted
a usb key to one port on this card. No extra power usage
appears, except for a small blip after the usb key is inserted.
The temperature of the CPU is unchanged. Under full load, the
max temperature is the same as when the key was inserted in
a built in port. After the application ends, the temperature
quickly returns to its idle value. We get a temperature change
of about 10 degree C from idle to full load using a number crunching
application. This probably makes most of the CPU active-integer, floating
point, and addressing.
I get the same behavior on another computer, built on an Asus
A8V which uses a K8T800Pro chipset. Both computers use an AMI
Bios and both use a VT8237 chip for USB. I guess it should not
be a surprise that they both display similar behavior on this issue.
Questions:
1. Has anyone else detected this behavior on these or other
motherboards?
2. Is it reasonable to assume that the behavior stems from some
implementation detail in the chipset/BIOS?
3. Why does the insertion of a usb key in a builtin port
require 30 watts more power from the CPU???? This is more than
half the increase from idle caused by loading the CPU with a large
numerical simulation application:)!
4. What is going on in the CPU that the CPU load meter does not
change even though 30 watts more power is being dissipated?
I currently plan to use PCI based USB ports for usb-storage
connections--I see no need to heat the CPU so much just to do
some I/O on the USB bus.
Thanks for any insight into this strange behavior. I don't believe
there is anything amiss in lm_sensors and that the problem lies in
the USB subsystem as implemented in the VIA chipset.
Delbert
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