Cannot change Intel turbo boost (/sys/devices/system/cpu/intel_pstate/no_turbo/ not accessible)

The turbo enabled or disabled flag can be misleading. Excerpt from Documentation/cpu-freq/intel-pstate.txtin the source tree:

Sysfs will show :
        max_perf_pct:100, which corresponds to 1 core ratio
        min_perf_pct:24, max_efficiency_ratio / max 1 Core ratio
        no_turbo:0, turbo is not disabled
        num_pstates:26 = (max 1 Core ratio - Max Efficiency Ratio + 1)
        turbo_pct:39 = (max 1 core ratio - max non turbo ratio) / num_pstates

So, in this case the "1" means turbo is disabled. For most computers, turbo can be disabled in the BIOS, in which case one can not override the indicator flag in Sysfs. Example 1 (turbo is disabled in the BIOS):

$ echo 0 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo
0
tee: /sys/devices/system/cpu/intel_pstate/no_turbo: Operation not permitted

Example 2 (turbo is enabled in the BIOS):

$ cat /sys/devices/system/cpu/intel_pstate/no_turbo
1
$ echo 0 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo
0
$ cat /sys/devices/system/cpu/intel_pstate/no_turbo
0