[123music]

What is Dhrystone MIPS?How is it different from normal MIPS and how do we calculate it?

[sim]

MIPS isn't generally considered a useful measure of performance - it's typically quoted based on choosing the fastest (likely one of the least capable) instructions on a machine, with no regard to the capabilities of that machine. Consider, if I built a machine that could only execute NOP, but could execute 200 million NOPs a second, it would be a 200 MIPS machine, however, if I built an entire fully feature CPU that could execute only 100 million NOPs per second (and NOP was the fastest instruction) but could also execute loads, stores, adds, multiplies etc. etc., it would be a 100 MIPS machine - however, the NOP-only machine appears (using the MIPS measure) to be twice as "good" despite being useless.

DMIPS is based on the time taken to execute a particular benchmark, something which might be considered representative of a real workload, namely Dhrystone. The DMIPS figure for a given machine is the relative speed a VAX 11/780 (a particular "1 MIPS" machine) would have to run at to complete the benchmark in the same amount of time as the machine being measured. For example, if a 100MHz CPU completes the benchmark 200 times faster than the VAX 11/780 does, then it would be considered a 200 DMIPS machine. For CPUs that can be run at various frequencies, then you'll often see this value reported divided through by MHz, e.g. 2 DMIPS/MHz in this example.

So, the quick answer is that (unlike MIPS) DMIPS can't be calculated, it can only be measured.

There are further details, and a link to the Dhrystone source code here: http://en.wikipedia.org/wiki/Dhrystone

hth
s.

This post has been edited by sim: 25 June 2010 - 08:35 AM

[123music]

Why are we going for this measurement ? What happens if we specify in terms of MIPS only..?
Recently i found that TMS570 ARM offers 250DMIPS. It means it is 250 times faster than VAX 11/780 machine?

Correct me if i am wrong.

[sim]

Pretty much, though as with any benchmark, it's only indicative of what that benchmark stresses, so strictly speaking it's 250x faster at running Dhrystone than the VAX. Dhrystone doesn't use floating-point, DSP etc., and R4F may be a further order of magnitude faster in these areas.

hth
s.