Chips and Cheese in a detailed article showcased the time taken by various microarchitectures from AMD and Intel to reach max frequencies.
How Do CPUs Increase Clock Speeds
CPUs need more power in order to increase their frequencies. Using the P=IV formula, we see as the voltage (V) increases, so does the power (P). Although, CPUs are vulnerable to spikes in voltage so the CPU needs to adjust the voltage smartly. All of this depends upon the microarchitecture and how well the CPU can switch back and forth between a high and a low voltage.
We are first greeted by the winner (As you probably saw from the title), AMD’s Zen3 architecture. Chips and Cheese used the Ryzen 7 5800U which goes from <2.0GHz to 3.7GHz in just 1.60ms (milli-seconds). However, the 4.4GHz Max Boost Clock was not achieved.
The predecessor to Zen3, Zen2 is slightly slower coming in at 9.35ms. The CPU used is the Ryzen 7 4800H which goes from ~1.3GHz to 4.3GHz after 9.35ms. The desktop R9 3950X (Good CCD) is slower at 16.32ms when clocking from 1.7GHz to 4.3GHz.
The FX-8350 from 2012 is based on AMD’s Piledriver microarchitecture. The CPU takes 47.72ms to increase its frequencies from 1.4GHz to 3.41GHz. However, on reaching 4.21GHz the time taken amounts up to a massive 79.32ms.
Chips and Cheese then used Windows power plan with the ‘minimum CPU state’ set at 100% causing the FX-8350 to stay at 1.35V all the time. The FX-8350 has all the volts available to itself and took just 0.18ms to reach 4.14GHz from 1.45GHz. That’s an insane improvement.
So basically, the delay we saw in other CPUs was due to the time taken to adjust the CPU voltage. The CPU cannot handle a voltage change from lets say 0.7V – 1.35V in such a short span of time. But, if the CPU is constantly running at a relatively high voltage, then the CPU clock ramp time decreases significantly.
As you can see, the Zen3 microarchitecture is at the top with insanely short CPU clock ramp times. However, if the voltage is adjusted properly, this CPU can be overtaken by the FX-8350. Either way, all credits go to Chips and Cheese for the time and effort put into these results. Take a look at their article for a much more detailed overview.