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Dhrystone and MIPs performance of ARM processors

Applies to: ARM Architecture and Instruction Sets

Answer

The MIPS figures which ARM (and most of the industry) quotes are "Dhrystone VAX MIPs". The idea behind this measure is to compare the performance of a machine (in our case, an ARM system) against the performance of a reference machine. The industry adopted the VAX 11/780 as the reference 1 MIP machine.

The benchmark is calculated by measuring the number of Dhrystones per second for the system, and then dividing that figure by the number of Dhrystones per second achieved by the reference machine.

So "80 MIPS" means "80 Dhrystone VAX MIPS", which means 80 times faster than a VAX 11/780.

The reason for comparing against a reference machine is that it avoids the need to argue about differences in instruction sets. RISC processors tend to have lots of simple instructions. CISC machines like x86 and VAX tend to have fewer, more complex instructions. If you just counted the number of instructions per second of a machine directly, then machines with simple instructions would get higher instructions-per-second results, even though it would not be telling you whether it gets the job done any faster. By comparing how fast a machine gets a given piece of work done against how fast other machines get that piece of work done, the question of the different instruction sets is avoided.

There are two different versions of the Dhrystone benchmark commonly quoted:

  • Dhrystone 1.1
  • Dhrystone 2.1

ARM quotes Dhrystone 2.1 figures. The VAX 11/780 achieves 1757 Dhrystones per second.

- The maximum performance of the ARM7 family is 0.9 Dhrystone VAX MIPS per MHz.
- The maximum performance of the ARM9 family is 1.1 Dhrystone VAX MIPS per MHz.

These figures assume ARM code running from 32-bit wide, zero wait-state memory. If there are wait-states, or (for cores with caches) the caches are disabled, then the performance figures will be lower.

To estimate how many ARM instructions are executed per second then simply divide the frequency by the average CPI (Cycles Per Instruction) for the core.

- The average CPI for the ARM7 family is about 1.9 cycles per instruction.
- The average CPI for the ARM9 family is about 1.5 cycles per instruction.

For more information, please see App Note 93: "Benchmarking with ARMulator".

Article last edited on: 2010-07-28 10:00:25

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