If we want to compare processor speed of CPU (inside MCU or MPU) how we can know which one is faster than another one? How can we know that?
The answer is we use relative comparison processor speed with reference CPU, what we call DMIPS (Dhrystone Million instructions per second or Dhrystone MIPS), reference CPU is DEC VAX 11/780 made since 1970. By comparison the same speed with DEC VAX 11/780 equal to 1 DMIPS. Relative comparison can use for compare with different Architecture CPU such as compare MSP 430 and ARM cortex M0 by DMIPS.
For Popular for compare speed unit is DMIPS/MHz. when ARM cortex M0 is 0.84 DMIPS/MHz and MSP430 is 2.1 DMIPS/MHz.
What about MIPS, Million instructions per second, which mean how many instruction can run in one second. For example CPU x can run NOP command 100 million in one second, which mean it has speed 100 MIPS. MIPS can use when you compare speed of CPU in the same CPU Architecture, if you has compare different Architecture with MIPS you will get result incorrect, different Architecture mean some instructions are use different CPU clock cycle.
Relative comparison speed of CPU not has only just DMIPS, other is CoreMark, offers by EEMBC (Embedded Microprocessor Benchmark Consortium) are nonprofit organization.
For more information about Source code Dhrystone MIPS you can study more at link below,