CPU Performance Evaluation Criteria

MIPs: million instructions executed per second
Dmips: dhrystone million instructions executed per second
Mflops: million floating-point operations per second
 
MIPs, dmips, and mflops are common CPU performance evaluation criteria. Note that MIPs is only suitable for evaluating scalar machines, while mflops is more suitable for measuring the performance of vector machines.
1. MIPS
How many million commands are executed per second

2. dmips
D, short for dhrystone, represents MIPS in a test method such as dhrystone, which is an integer operation test program.
Using dmips to measure CPU performance has major defects. Dmips do not mean millions of commands per second. Instead, they run a benchmark program called dhrystone, showing a relatively high performance unit, in many cases, people are also used to using MIPS as the unit of this performance indicator. Because Program-based testing is vulnerable to malicious optimization and the release of dmips indicators is not monitored by any organization, you must be careful when using dmips for evaluation.

Arm has always adopted a relatively conservative value as the CPU dmips nominal value. Another disadvantage of dmips is that it cannot measure the processor's digital signal processing capability and the performance of the cache/MMU subsystem. Because the dhrystone test program does not contain DSP expressions, it only contains integer operations and string processing, and the test program is too small, it can be almost completely put into the cache to run without interacting with external memory. In this way, it is difficult to reflect the real performance of the processor in a real system.

Dmips calculation method: dhrystone tries to represent the result more meaningfully than MIPS (million instructions per second), because MIPS cannot be used into SS different instruction sets (e.g. RISC. CISC) for the same Computation
Requirement from users. thus, the main score is just dhrystone loops per second. another common representation of the dhrystone benchmark is the dmips-dhrystone MIPS-obtained when the dhrystone score is divided by 1,757 (the number of dhrystones per second
Obtained on the VAX 11/780, nominally a 1 MIPS machine ).

For the same computing program, the number of commands generated on machines with different instruction sets (such as CISC and RISC) is different. In this case, comparison with MIPs is meaningless, it makes sense to use dmips for comparison. The number of commands generated on machines with the same instruction set is the same (the compiler and libc are the same). It makes sense to use MIPS for comparison.

3. mflops

It is a CPU test program based on floating point operations. Of course, the results of this test are also expressed by mflops, representing the CPU's ability to process floating point operations.

4. Summary

The CPU Performance Evaluation adopts a comprehensive test program. The popular ones are whetstone and dhrystone. Dhrystone is mainly used to measure the integer computing capability, measured in dmips. Whetstone is used to measure the floating point computing capability. The unit is mflops.