DVFS capabilities in latest Intel processors

Karthik_Vadambacheri — Sun, 05 May 2013 22:04:12 GMT

Hi,

I would like to know whether we can change the frequency of the intel multi-core processors individually. I have Intel Core2Duo CPU T5750 which has 2 cores. When I run cpufreq-info in Linux I get to know that both the cores will run in the same hardware frequency. Please find cpufreq-info output below(Relevant data shown)

$ cpufreq-info
*******************
analyzing CPU 0:
driver: acpi-cpufreq
CPUs which run at the same hardware frequency: 0 1
CPUs which need to have their frequency coordinated by software: 0
maximum transition latency: 10.0 us.
hardware limits: 1000 MHz - 2.00 GHz
available frequency steps: 2.00 GHz, 1.67 GHz, 1.33 GHz, 1000 MHz
********************

********************
analyzing CPU 1:
driver: acpi-cpufreq
CPUs which run at the same hardware frequency: 0 1
CPUs which need to have their frequency coordinated by software: 1
maximum transition latency: 10.0 us.
hardware limits: 1000 MHz - 2.00 GHz
available frequency steps: 2.00 GHz, 1.67 GHz, 1.33 GHz, 1000 MHz

Hence by above output I expect both cores to vary its frequency in a synchronous fashion.

But when I tried to check the frequency of each core by using the information in /proc/cpuinfo, I see that the cores are varying its frequency individually. The command I used and its output are below:

$ while true; do grep -e "cpu MHz" /proc/cpuinfo; echo "===";sleep 0.1; done

cpu MHz : 1000.000
cpu MHz : 1000.000
===
cpu MHz : 2000.000
cpu MHz : 1000.000
===
cpu MHz : 1000.000
cpu MHz : 1000.000
===
cpu MHz : 1000.000
cpu MHz : 1000.000
===
cpu MHz : 1000.000
cpu MHz : 2000.000
===
cpu MHz : 1000.000
cpu MHz : 1000.000
===
******************

******************

The above output can be more neatly obtained using watch command as below:

$ watch -n 0.1 grep \"cpu MHz\" /proc/cpuinfo

My questions are:

1) Can someone explain why the cores change the frequency individually even though the cpurfreq-info says that both the cores run at the same hardware frequency? Am I missing something?

2) Does latest intel multi-core chips have per-core DVFS? Kindly let me know.

3) Can voltage and frequency can be changed independent of each other in latest multicore processors using EIST (Enhanced Intel Speed Step Technology)?

Kindly let me know your comments...

Thanks for your time,

Karthik.V.M.

Hi Karthik,

Harold_G_Intel — Wed, 08 May 2013 16:11:47 GMT

Hi Karthik,

You may want to repost this on the Community for processors here: http://communities.intel.com/community/tech/processors

Regards, Hal G

Intel(R) Developer Zone Support

http://software.intel.com
*Other names and brands may be claimed as the property of others.

Hi Hal,

Karthik_Vadambacheri — Fri, 10 May 2013 00:31:30 GMT

Hi Hal,

Thanks a lot for your assistance. I will repost it there.

Regards,

karthik

topic DVFS capabilities in latest Intel processors in Software Archive

DVFS capabilities in latest Intel processors

Hi Karthik,

Hi Hal,