Re: Is /proc/acpi/thermal_zone/THM0/temperature reliable?
- From: ibuprofin@xxxxxxxxxxxxxxxxxxxxxx (Moe Trin)
- Date: Tue, 29 Apr 2008 23:00:27 -0500
On Mon, 28 Apr 2008, in the Usenet newsgroup comp.os.linux.hardware, in article
<1470d781-dab6-462f-9ae8-c6e62a980f46@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, Yong Huang
wrote:
NOTE: Posting from groups.google.com (or some web-forums) dramatically
reduces the chance of your post being seen. Find a real news server.
$ uname -a
Linux <hostname> 2.6.9-55.EL #1 SMP Fri Apr 20 16:30:19 EDT 2007 ia64
ia64 ia64 GNU/Linux
cat /etc/*release /etc/*version
$ cat /proc/acpi/thermal_zone/THM0/temperature
temperature: 27 C
That looks good. But I've monitored it for a few weeks once per minute
on four servers that have the same hardware. The temperature is always
27C. That makes me wonder if the number is really the actual
measurement.
HIGHLY unlikely.
# rpm -qa | grep lm_sensors
#
I take that to mean the lm_sensors packages are not installed.
You'll want to read the Intel documentation on the temperature sensing
diode in the CPU, and documentation from your motherboard and/or chipset
supplier to read about the on-board thermal sensors (thermistors).
BRIEFLY - neither is "accurate". The CPU temperatures are measured as
a voltage drop across a diode passing a specified amount of current.
How accurate is the current "set"? How accurately is the voltage drop
measured? The answer is that nothing is checked, other than a gross "is
it alive" type of check. Accuracy is dependent on how accurately the
materials were fabricated. The best you can do is make relative
measurements - it was 33C at idle yesterday when the room temperature
was 25C/77F, and today it reads <mumble>. Further, the CPU temp is
the local temperature at a point on the die - it's not the hottest
or coolest point. As far as the other (non-CPU) temperatures,
the absolute accuracy is even worse, as the thing they are looking at
(the change in resistance of a blob of metal oxides verses ambient
temperature) depends on the mixture of those oxides, the amount of
oxides, the composition of the mechanical coating that is used to
package the device. The resistance at a reference temperature (usually
25C) is subject to a 10 to 20 percent tolerance, and the rate at which
the resistance changes is subject to a similar additional tolerance.
The manufacturers can only afford to see that the devices are "alive".
The cost of actually testing the accuracy is far to much for a consumer
product - never mind actually calibrating things to some specification
of accuracy.
Bottom line - don't look at absolute values. Look at changes in the
reported values.
Old guy
.
- References:
- Is /proc/acpi/thermal_zone/THM0/temperature reliable?
- From: Yong Huang
- Is /proc/acpi/thermal_zone/THM0/temperature reliable?
- Prev by Date: Fujitsu-Siemens CELSIUS W360 and Linux setup problem - a solution
- Next by Date: asrock mobo - raid sata disks
- Previous by thread: Re: Is /proc/acpi/thermal_zone/THM0/temperature reliable?
- Next by thread: Fujitsu-Siemens CELSIUS W360 and Linux setup problem - a solution
- Index(es):
Relevant Pages
|
