Processor BenchMark Utility

PeterGlen

4.09/5 (9 votes)

May 29, 2008

CPOL

4 min read

39521

754

Measuring Processor Performance

Introduction

This article discusses a processor benchmark utility. The results are surprising. Just as everything else (these days) breaks our preconceptions, so do processors.

Just the other day, I received an email about 21^st century's broken preconceptions. It went something like this " .... the tallest basketball player is Chinese ... the most popular rapper is white, and the best golf player is ....". So there is little or no surprise to see a processor benchmark that shatters preconceptions.

Background

I was always curious about how the new generation processors measure up. How fast are they? Not just a number that represents the processor as a whole, but a real value that represents an honest measure of how many operations of a given kind the processor can do in a given time. For instance, how many integer additions a second. How many double divides a second? ....

Using the Code

The code is developed to use macros as the instrument of simplification. This way, the macro parameter can signify any desired benchmarking operation. The macro TIMEDOP (timed operation) is called with two parameters:

The name of the function to generate
The code to execute in the timing loop

//
// The timing loop generation macros. You may roll your own by changing the second
// argument to the macro to a piece of code. 
// If you use variables in the code snippet, make sure you declare them first.
//
// Here is an example of tinkering between add and increment:
//
//    TIMEDOP(do_int,        count2++   );
//    TIMEDOP(do_int,        count2 +=3 );
//
// Note the missing (or optional) semicolon (;) at the end of the snippets.

TIMEDOP(do_int,        count2++);
TIMEDOP(do_mul,        count *= 33);    // I chose the constants randomly
TIMEDOP(do_div,        count /= 13);    // they have no influence on the timing
TIMEDOP(do_sub,        count -= 10);
TIMEDOP(do_mod,        count %= 13);
TIMEDOP(do_str,        memcpy(str, str2, 1024));
TIMEDOP(do_str2,       memcpy(str, str2, 1));
TIMEDOP(do_dbladd,     dop2 += dop1; dop1+=3);
TIMEDOP(do_dbladd3,    dop2 = dop1 + dop3; dop1+= 2);
TIMEDOP(do_dbldiv,     dop2 /= 103);
TIMEDOP(do_dblsin,     dop2 = sin(dop1); );
TIMEDOP(do_func,       noop(count2));
TIMEDOP(do_cos,        cos(dop1););
TIMEDOP(do_tan,        tan(dop1););
TIMEDOP(do_sqrt,       sqrt(dop1););

// After declaring, one may call the function as follows:

int count = do_int();  // count receives the count of instructions / 100

// To make sure the time elapsed is accurate, the performance counter is 
// queried twice, as to measure how long it takes to query the performance counter.

QueryPerformanceCounter(&PerformanceCount);\
double dd = largeuint2double(PerformanceCount);\

QueryPerformanceCounter(&PerformanceCount3);\
double skew = largeuint2double(PerformanceCount3) - dd;\
         
// Then, in the main loop, every time the performance counter is
// queried, the code extends the expected time by the time it 
// took the performance counter to respond

... in the while loop ...

timeforonesec += skew;  /* Compensate for skew */
if(currentcount - startcount > timeforonesec)  
    break;

Accuracy of the Measurement

Naturally, there are a lot of processes that compete for the processor. Thus, the benchmark measured flutters quite a bit. To compensate for that, the utility keeps a running average.

To test the accuracy of the code, and to prove if the compensatory trick works as intended, I was in a bit of a dilemma. The old Heisenberg principle kicked in, I could not observe the processor speed, as the observer process interfered with the findings. In other words, anything I tried to do with the processor interfered with the measurement.

Finally, in an idea to test the compensation code, I executed the benchmarking code snippet (from a macro) one hundred times in one test, and fifty times in the other test. If the compensating code works correctly, the results of the second test should be twice as large as the first test. It worked! Hurray!

I thought about the fact that measuring the processor speed involved a theory developed in connection with quantum mechanics. Very COOL. Isn't this what programming is all about?

Benchmark Items Described

The following is a short synopsis of the items on the benchmark screen:

Function Name Code Description Notes

do_int, count2++ Simple integer addition and/or increment Increment and add at the same speed

do_mul, count *= 33 Simple integer multiplication Almost as fast as the add

do_div

count /= 13

Simple integer division

Slower than double add

do_mod count %= 13 Simple integer modulus Same speed as div

do_str memcpy(str, str2, 1024) Copy a 1k string Involves memory. Nice test to see if the DDR 400 upgrade worked.

do_str2 memcpy(str, str2, 1) Copy a 1 byte string Library call overhead

do_dbladd dop2 += dop1; dop1+=3 add two doubles the optimizer knew bout the second var not changing., so we padded it.

do_dbladd3 dop2 = dop1 + dop3; dop1+= 2 add two doubles, assign padded as well

do_dbldiv dop2 /= 103 double divide faster than integer op

do_dblsin dop2 = sin(dop1) trigonometric slower than expected

do_func noop(count2) call a blank function debug build a lot slower

do_cos cos(dop1) trigonometric all trig functions execute with similar speed

do_tan tan(dop1) trigonometric

do_sqrt sqrt(dop1) square root the processor works hard here

The Debug Build

The debug build has similar performance as the release build. The only significant difference is in the function calls. This is (possibly) due to the overhead of the debugger keeping tabs on the function call stack.

The Release Build

We had to disable optimization, as it breaks the code (naturally). The optimizer knows that we are making repeated calculations and repeated calls for no reason, so it optimizes it out.

Points of Interest

I have examined several processors with this utility (Core2, Sempron, AMD_64). To my surprise, I have found most of the adages learned in the past are broken. For example, when learning C or C++, one finds the recommendation that: 'variable++' is faster than 'variable += 1'. According to the benchmarks, var1 += var2 is the same speed as var1++;.

Another common knowledge is that working with doubles is slower than integers. Not according to the results of the benchmark. On my Athlon 64, the int divide is 45000/sec and the double divide is 153000/sec.

The integer multiply is just as fast as adding. Another unexpected result.

If all this sounds unbelievable, by all means, test it for yourself. Try the code, and if the code is in err, I would like to hear about it.

Feedback

Send me your processor's screen shot (peterglen@verizon.net).

History

29^th May, 2008: Initial version