▷ What is the processor ipc

In today's computers, instructions per cycle, or also known as IPCs, are a very important aspect of processor performance. This concept represents the average number of instructions executed for each processor clock cycle, so the higher it is, the more powerful the processor will be. In this article we explain everything relevant about the CPI.

Index of contents

What is the processor CPI, how is it calculated and how important is it?

The IPC calculation is done by running a set of code, calculating the number of machine-level instructions required to complete it, and then using high-performance timers to calculate the number of clock cycles required to complete it on real hardware.. The end result comes from dividing the number of instructions by the number of CPU clock cycles.

The number of instructions per second and the floating point operations per second for a processor can be derived by multiplying the number of instructions per cycle with the clock speed (cycles per second given in Hertz) of the processor in question. The number of instructions per second is a rough indicator of the likely performance of the processor.

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The number of instructions executed per clock is not a constant for a given processor, as it depends on how the particular software being executed interacts with the processor and, indeed, with the whole machine, particularly with the memory hierarchy. However, certain processor characteristics tend to lead to designs that have above-average IPC values, such as the presence of multiple arithmetic logic units and short pipes. When comparing different instruction sets, a simpler instruction set can lead to a higher IPC figure than implementing a more complex instruction set, which uses the same chip technology, however the more instruction set complex can accomplish more useful work with fewer instructions.

Factors governing the CPI

A given level of instructions per second can be achieved with a high IPC and low clock speed (such as the AMD Athlon and early Intel Core series), or from a low IPC and high clock speed (such as the Intel Pentium 4). Both are valid processor designs, and the choice between the two often depends on history, engineering constraints, or marketing pressures. However, a high IPC with high frequency provides the best performance.

Cycle instructions for multiple processors.

These numbers are not the IPC value of these CPUs, but represent the theoretically possible floating point performance. Please note that the numbers below only represent the logical widths of the processor's SIMD drives. They do not account for the multiple SIMD pipes present in most architectures, nor do they represent the main architectural definition of IPC, which measures the number of average scalar instructions removed per cycle, both integers, floating points, and control.

CPU	Double precision DP IPC	Simple precision SP IPC
Intel Core and Intel Nehalem	4	8
Intel Sandy Bridge and Intel Ivy Bridge	8	16
Intel Haswell and Intel Coffee Lake	16	32
Intel Ice Lake	?	?
Intel Xeon Skylake (AVX-512)	32	64
AMD K10	6	12
AMD Bulldozer, AMD Piledriver, and AMD Steamroller	12	24
AMD Ryzen	16	32
Intel Atom (Bonnell, Saltwell, Silvermont and Goldmont)	two	4
AMD Bobcat	two	4
AMD Jaguar and Puma	4	8
ARM Cortex-A7	one	8
ARM Cortex-A9	one	8
ARM Cortex-A15	one	8
ARM Cortex-A32	two	8
ARM Cortex-A35	two	8
ARM Cortex-A53	two	8
ARM Cortex-A57	two	8
ARM Cortex-A72	two	8
Qualcomm Krait	one	8
Qualcomm Kryo	two	8
IBM PowerPC A2	8	SP elements extend Ed to DP and processed in the same units
IBM PowerPC A2	4

To get a theoretical GFLOPS rating (billions of FLOPS) for a given CPU, multiply the number in this table by the number of cores, and then by the value clock (in GHz) of a particular CPU model. For example, a Coffee Lake i7-8700K theoretically handles 32 single precision flops per cycle, it has 6 cores and a base clock of 3.7 GHz. This gives you 32 x 6 x 3.7 = 710.4 GFLOPS.

It is important to note that multithreading does not mean that two threads can operate on the same core simultaneously, sharing pipeline resources. Instead, the CPU allows one thread to use the kernel, while another waits for the data to come from memory, as in the case of a lack of cache. The operating system developer can return the original thread to the queue, and then return to the CPU once the data has been recovered.

Therefore, this feature has no effect on a CPU's theoretical floating point performance, but in certain cases it can help the CPU get closer to that performance, in multiple threads, in practice. Generally, the large processor log shows how large processor numbers can count once. The number of records is also important, as they can be connected together for a moment with some instructions.

The IPC is not the only thing that matters on a PC

The useful work that can be done with any PC depends on many factors besides the speed of the processor. These factors include instruction set architecture, processor microarchitecture, and organization of the computer system, such as the design of the disk storage system and the capabilities and performance of other connected devices, the efficiency of the operating system, and most of all, importantly, the software.

For users and buyers of a computer system, clock instructions are not a particularly useful indication of the performance of their system. For an accurate measure of performance relevant to them, application benchmarks are much more useful. Knowledge of their existence is useful as it provides an easy-to-understand example of why clock speed is not the only factor relevant to equipment performance.

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So far our article on what the processor IPC is, we hope you find it very useful.

Wikipedia source