How can I detect a throttled clock in software

mookNOW · 06-03-2010, 10:47 AM

I'm running on a Xenon L5408 and my OS is CentOS 5.4. The system I'm developing needs to be able to run in a room that *may* get rather hot.

When the core temperatures gets up to around 99DegC I get the following message sent to the terminal. "temperature above threshold cpu clock throttled". So Linux some how knows whats going on.

So I'm now running in a degraded state. My question is, from an application I'm writting (c++), how would I go about detecting a throttled clock.

Many Thanks,

troop · 06-03-2010, 10:52 AM

you can read kernel messages via /proc file system: /proc/acpi/processor/CPU0/throttling

mookNOW · 06-04-2010, 04:15 AM

Thanks for the reply. I've looked at this file and it says <not supported>

Further looking round on the web and I see that "/proc/acpi is being replaced by interfaces in /sys and new software should not look in /proc." (ref- http://acpi.sourceforge.net/document...processor.html)

But I can't find a throttling under /sys. Do you know where the correct version is? Or is it not supported in my OS?

syg00 · 06-04-2010, 04:54 AM

Why do you care ?.
Strictly speaking the CPU (core) is running degraded, not what we normally think of as "the clock" from a userspace perspective. It's possible the CPU could drop into different states at any time, not just from temp.

mookNOW · 06-04-2010, 06:16 AM

I want to be able to log (in my own logfile) when the CPU is running degraded to help with diagnosing the events the happened before the throttling occured.(Maybe a fan failed just before the throttling)

It might also enable me to stop processors intensive but none critical applications in the system.

Also, I'd like to know to what extent its throttling. Looking at the link I've gave above it appears the throttling can be in various state (of forced sleeping)

troop · 06-04-2010, 11:46 PM

Quote:

Further looking round on the web and I see that "/proc/acpi is being replaced by interfaces in /sys and new software should not look in /proc." (ref- http://acpi.sourceforge.net/document...processor.html)

But I can't find a throttling under /sys.

/sys/devices/system/cpu/cpu0/thermal_throttle/throttle_count

mookNOW · 06-07-2010, 03:52 AM

the contents of /sys/devices/system/cpu/cpu0 on my machine is...

cache
cpufreq
crash_notes
topology

I don't seem to have a thermal_throttle directory. Is there something I need to active in the operating system?