Frequently Asked Questions

What does effective frequency mean?

Effective frequency is a virtual frequency value used for power measurement of processors to characterize the resulting processing speed. This takes into account that

• a processor may change its clock frequency during measurement,
• the work may be distributed onto several processors and
• a processor might not have enough jobs during measurement to keep it busy all the time.

Based on the observed clock frequencies, an average value is calculated weighted by the respective duration, where an idle processor is equivalent to a duration of zero. The resulting value is then averaged once again across all processors.

Consider, for example, 2 processors, the first of which runs at 2000 MHz without any change in clock speed, the second runs unchanged at 1000 MHz. On the first, we load processes that utilize it to 20%, the second is put under a load of 60%.

The effective frequency of the first processor is 2000 × 0.2 = 400 MHz, that of the second 1000 × 0.6 = 600 MHz. The overall system has an effective frequency of (400 + 600) ÷ 2 = 500 MHz.

This means that in this situation, the two processors could have been replaced by a single one that would have run continuously under full load at 500 MHz. It would have provided exactly the same computational power.