CPU frequency increases with GPU used with Sandy-Bridge

Hello,

We are using a core i7 Sandy-bridge with LINUX with the CPU frequency fixed (governor mode = user_space) at 1.2Ghz.

When we read the CPU frequency with /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq we read 1.2Ghz

If we launch X server with "startx" command and after using the GPU, we see the cpu frequency raises to 1.6Ghz ! But if we set the CPU frequency from 1.6Ghz to 2.1Ghz the CPU, frequency remains at the value fixed (i.e 1.7Ghz)!

We don't used Turbo Boost, HT or others BIOS setting allowing to improvement of the CPU and/or GPU.

In all case I expected that the CPU Frequency could drop if GPU needs more perfomance and/or thermal management needs to decrease frequency but not increase the CPU frequency when this frequency is fixed by user.

Thanks for your help.

Regards