Frequency per core on Xeon Phi

[Sun_L_1]

Hello there,

Did the frequency value of each core is the same as each card's frequency on Xeon Phi? Is that possible to get frequency per core for Xeon Phi? Thanks.

[JJK · Accepted solution]

In 99% of all configurations all cores will run at the same frequqency.

However, as the Xeon Phi runs linux it is possible to tweak the frequencies using some /sys/device/system settings. The default 'scaling_governor' seems to be "performance" which means that all cores will always run at top speed. If you set the scaling_governor to 'ondemand' then the cores frequencies will scale up and down, depending on the load.

$ echo ondemand > /sys/devices/system/cpu/cpu0/scaling_governor

### run a simulation

$ grep MHz /proc/cpuinfo | sort -u
cpu MHz         : 619.047
cpu MHz         : 952.380

You can query the freqency of a single core by looking at either /proc/cpuinfo, which lists all 200+ cores or by looking at /sys/devices/system/cpu/cpuN/cpufreq/cpuinfo_cur_freq

[Sun_L_1]

Hi JJK,

Thanks for the reply, that's really helpful!

[Frances_R_Intel]

I did not know about the scaling_governor, so JJK has taught me something. In looking at my own system, I saw that, on the coprocessor, the file is /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor. I don't know what effect, if any, changing scaling_governor to ondemand will have and if you change that value on the coprocessor, that change will disappear on reboot, for two reasons - 1) changing the file on the coprocessor does not change the value in the base files on the host which are used to boot the coprocessor, 2) cpu frequency is one of the boot parameters that the mpss sets on each boot and that which is set by changing the mic0.conf file and the only choices are cpufreq_on (which, on my system, stores the value 'performance' in the scaling_governor file) and cpufreq_off (which removes the file scaling_governor).