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View Full Version : [ubuntu] The performance governor for cpufreq doesn't seem to behave as advertised



mgoldshteyn
August 23rd, 2012, 07:57 PM
The kernel in use: 3.2.0-23-generic on Ubuntu 12.04LTS
For example, I issue the following command:

sudo cpufreq-set -c 0 -g performance
Then I go to /sys/devices/system/cpu/cpu0/cpufreq and type in the following:

sudo cat cpuinfo_cur_freq
Sometimes I get the max frequency (3600 MHz) when I do this and sometimes I get the min frequency (1600 MHz).
If I do:

cat scaling_governor
The output is performance, showing that the governor is in fact set to performance.
Then, to make it even more weird, if I do:

cpufreq-info
I get:


analyzing CPU 0:
driver: acpi-cpufreq
CPUs which run at the same hardware frequency: 0 1 2 3 8 9 10 11
CPUs which need to have their frequency coordinated by software: 0
maximum transition latency: 10.0 us.
hardware limits: 1.60 GHz - 3.60 GHz
available frequency steps: 3.60 GHz, 3.60 GHz, 3.47 GHz, 3.33 GHz, 3.20 GHz, 3.07 GHz, 2.93 GHz, 2.80 GHz, 2.67 GHz, 2.53 GHz, 2.40 GHz, 2.27 GHz, 2.13 GHz, 2.00 GHz, 1.87 GHz, 1.73 GHz, 1.60 GHz
available cpufreq governors: conservative, ondemand, userspace, powersave, performance
current policy: frequency should be within 3.60 GHz and 3.60 GHz.
The governor "performance" may decide which speed to use
within this range.
current CPU frequency is 3.60 GHz.
...

If you look at the current policy above, you will notice that it is telling me that the CPU should be pegged at 3.60 GHz. Yet, polling (i.e., displaying) cpuinfo_cur_freq once a second seems to tell a different story.

Doug S
August 23rd, 2012, 08:29 PM
I don't actually use the cpufrequtils package, and don't even have it installed.
However, and due to some specific work I have being trying to help with, I have been constantly forcing CPU frequencies on a test machine for many many months now. As long as I wait long enough after system boot (on the order of a couple of minutes), I have found that what I ask for is what I always get. This includes way back with kernel 3.2.0.23-generic.
I realize my reply doesn't help you much.

mgoldshteyn
August 23rd, 2012, 08:50 PM
My results are hours after the system was rebooted. So, sadly, this is not a timing issue...

Doug S
August 23rd, 2012, 10:06 PM
I wonder if your CPU 0 is being throttled back because it is getting to hot?