Keep in mind that the formula for consumption in a processor is as follows:
Consumption = Capacity * Clock frequency * Square voltage
Because a processor’s capacity is a constant, the variables used to fluctuate power consumption, measured in watts (W), are clock frequency and voltage. The relationship between the two is that the higher the clock speed we want to achieve, the higher the voltage we need, so the increase in consumption is not linear, but rather exponential.
Now we can see that the same clock speed can be achieved by different voltages and that it is ideal that the consumption has the lowest value, although this is counterproductive in the face of temporary increases in the speed of the clock. ‘clock, because top speed may not be achievable without using a higher value.
What is the ACPI standard?
To understand the different consumption states of an Intel processor, you must first understand how the ACPI standard works, acronyms which mean Advanced configuration and power interface (ACPI) which would result in advanced settings and a power interface. This gives the operating system the following capabilities:
- Explore and discover new components or devices connected to I / O interfaces. This also allows Plug and Play and Hot Swapping.
- Control energy consumption, which allows them to vary the clock speed and the voltage consumed by each of them.
- Have the ability to put the processor and the various hardware components to sleep.
- It is essential for monitoring software and hardware.
It is an existing standard in processors since 1996 and defines the following global states for consumption on a PC:
- G0: the computer is operating at one hundred percent of its capacity.
- G1: the system is on standby, so it is switched on, consuming as little as possible
- G2: the system is idle, but the software execution has stopped completely, so there is no background execution.
- G3: When this state is activated, the whole computer turns off.
In this article, we will talk about what happens when the computer is in G0 mode and therefore we will not take into account the sleep or hibernation modes set through C states. More than anything because we think it is important. to shatter the myth of the high consumption of Intel processors.
The P-States and the consumption of Intel processors
For the P-States to be active, the PC must be in state G0 and therefore C0, where we are talking about the CPU being executed and therefore executing code. That is to say the usual use of the CPU where it has access to all the energy that the power supply can give it via the motherboard
According to the original ACPI standard, the operating system, which is in charge of managing the various processes, must be in charge of managing the power of the processor, although from the Intel Sky architecture Lake, significant changes were made and the P-States were no longer controlled by the operating system to be a hardware unit responsible for transitioning from one state to another, taking information from the internal MEMS to do so.
The number of P states varies by processor and ranges from the lowest clock speed using a single core to one using all cores at the highest possible clock speed. We have to take into account that the total clock speed is obtained from a base frequency which can be multiplied several times, so that a random clock speed will not be taken, but the multiplier will vary according to needs.
P-States make processors more efficient
As you can see in the graph above which is an illustrative example, the power consumption of Intel processors in each of the P-States is closely related to voltage and remember this is related to speed of ‘clock, but de In order to achieve greater efficiency, an additional variable is used.
Well, neither more nor less than the workload of the CPU and since this is where it executes instructions, the workload is defined from the start by the amount of instructions it has to execute. What is happening today is that we have multitasking environments where multiple programs and their processes are running simultaneously at the same time and in multi-core systems, so we have different workloads that are distributed among the different cores. .
As the operating system assigns these processes to different cores, it knows its level of workload on each. However, it is not what each instruction does, but also how much each consumes during execution is kept under lock and key.Today in the CPU there is a series of hardware units ordered for this. This technology is essential for reducing the consumption of Intel processors and making them more efficient depending on the applications you are running.
And what defines each P-State? Well, the number of active cores, clock speed and voltage in each of them, of course having a processor for gaming is like having a super sports car and you don’t want that. There is a speed limit, especially if you are competing or in our case running a high-performance application such as games.
What are PL1, PL2 and PL4 on Intel processors?
The maximum consumption of Intel processors is marked by the Power Limit constants which mark the limit in watts that a processor can consume, PL1 being the normal limit that the CPU can reach for 100% of the time.
As for the PL2, many of you will have observed that there is a Boost frequency, which in Intel processors is called Turbo and that is that roughly the analogy with a super sports car is ideal for understanding this, since it gives the processor extra power over time for a limited time, increasing your clock speed during the same time, in total up to 100 seconds.
The PL4 mode on the other hand corresponds to a micro acceleration, of only 10 microseconds, so only for a few instructions and to reach speeds much further, which due to their height, are not sustainable for the processor in the long term. It is not a commonly used mode and Intel has barely documented it.
PL1 = PL2 on Intel Core 12, what impact on consumption?
One change Intel made to its Alder Lake-S architecture is that PL1 = PL2, a statement that caused a lot of confusion due to the fact that in the company’s previous CPU architectures, PL2 mode lasted until to 100 seconds during which the consumption graph made a bridge in which the consumption first increased gradually, a good time was maintained in PL2 and then gradually decreased in PL1.
Let’s say there is a possibility in CPUs with Alder Lake-S architecture to run the processor in PL2 mode as if it were PL1 mode and the maximum clock speeds can be achieved without limit of time. Which has obvious consequences for durability and CPU consumption, but that’s why we previously explained P-States.
It should be borne in mind that with regard to the consumption of Intel processors, the PL allocated to each processor is a limit and this limit is not always reached, therefore the CPU will vary its clock speed. and its voltage according to its needs and they will not always consume this maximum. There are even units that when not in use are either turned off or have their clock speeds lowered so that they consume less.
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