Why is the frequency of the CPU lower than the Max. Boost Clock？

Question

I am using AMD's EPYC 7713 CPU. According to the specification, its maximum frequency is 3.675GHz. But when I run stress-ng (only running single threaded cpu loads), its frequency does not exceed 3.1GHz.

Performance counter stats for 'stress-ng --cpu 1':

   9537.779297      task-clock (msec)         #    1.000 CPUs utilized
            11      context-switches          #    0.001 K/sec
             0      cpu-migrations            #    0.000 K/sec
         6,913      page-faults               #    0.725 K/sec
29,506,467,746      cycles                    #    3.094 GHz <= lower than 3.675GHz
    79,241,572      stalled-cycles-frontend   #    0.27% frontend cycles idle
   526,975,722      stalled-cycles-backend    #    1.79% backend cycles idle
68,149,536,059      instructions              #    2.31  insn per cycle
                                              #    0.01  stalled cycles per insn
13,321,466,371      branches                  # 1396.705 M/sec
    71,660,522      branch-misses             #    0.54% of all branches

   9.538411830 seconds time elapsed

Why its frequency lower than expected?

Answer 1

Processors do not run at their maximum frequency all the time. The processor automatically selects the best frequency depending on the workload demand. If workload demand is high and there are no physical constraints, then the processor may operate at or close to the turbo frequency.