c - which code is consuming less power?

Question

My goal is to develop and implement a green algorithm for some special situation. I have developed two algorithms for the same.

One is having large no. of memory accesses(load and store). The pattern is some time coalesced and some time non-coalesced. I am assuming a worst case where most of the access will result in cache failure. See sample Code snippet a).

Another is having large no. of calculations, roughly equivalent to the code snippet b) below.

How do I estimate power consumption in each case. Which one is more energy efficient and why?

Platform: I will be running these codes on Intel I3 processor, with Windows 7, with 4 GB DRAM, 3 MB Cache.

Note: I do not want to use any external power meter. Also please ignore if you find the code not doing any constructive job. This is because it is only fraction of the complete algorithm.

UPDATE:

It is difficult but not impossible. One can very well calculate the cost incurred in reading DRAMs and doing multiplications by an ALU of the CPU. The only thing is one must have required knowledge of electronics of DRAMS and CPU, which I am lacking at this point of time. At least in worst case I think this can very well be established. Worst case means no coalesced access, no compiler optimization.

If you can estimate the cost of accessing DRAM and doing a float multiplication , then why is it impossible for estimating the current, hence a rough idea of power during these operations? Also see me post, I am not asking how much power consumption is there, rather I am asking which code is consuming less/more power or which one is more energy efficient?

a) for(i=0; i<1000000; i++)

  {

  a[i]= b[i]; //a, b floats in RAM.  

  {




 b) for(i=1; i<1000000; i++)

  {

   float j= j * i;  //j has some value. which is used later in the program , not  
                    // shown here    

  {

Answer 1

To measure the actual power consumption you should use add an electricity meter to your power supply (remove the batteries if using a notebook).

Note that you will measure the power consumption of the entire system, so make sure to avoid nuisance parameters (any other system activity, i.e. anti-virus updates, graphical desktop environment, indexing services, (internal) hardware devices), perform measurements repeatedly, with and without your algorithms running to cancel out "background" consumption. If possible use an embedded system.

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Concerning your algorithms, the actual energy efficiency depends not only on the C code but also on the performance of the compiler and also the runtime behavior in interaction with the surrounding system. However, here are some resources what you can do as developer to help on this:

• Energy-Efficient Software Checklist
• Energy-Efficient Software Guidelines

Especially take a look on the paragraph Tools in above "Checklist", as it lists some tools that may help you on rough estimates (based on application profiling). It lists (besides others):

• Perfmon
• PwrTest/Windows Driver Kit
• Windows Event Viewer (Timer tick change events, Microsoft-Windows-Kernel-PowerDiagnostic log)
• Intel PowerInformer
• Windows ETW (performance monitoring framework)
• Intel Application Energy Toolkit