Cycles-Nanoseconds-Counter

This project shows how to measure the performance of a C++ code by measuring the total execution time either in nanoseconds (ns) or CPU cycles. Currently its tailored for Cortex-A72 32 bits - 64 bits (both nanoseconds + CPU cycles), and Intel CPUs (nanoseconds).

The CPU cycle counter section of this repository is hugely based on the repository of Matthias J. Kannwischer (@mkannwischer) and @vincentvbh: https://github.com/mupq/pqax

Benchmarking

First, you must enable access to the performance counters from user mode. To do so:

cd enable_ccr
make
make install

If you get an error while running make, then update and upgrade your system. Also, you might need to install the kernel headers. To do so, run:

sudo apt install raspberrypi-kernel-headers

Code build and execution

The repository has two files: Main.cpp and Makefile.

To build the code, inside the folder containing these files, just run

make clean
make

This will generate a test file, which you can then execute by running

./test

Measuring CPU Cycles vs. Nanoseconds Execution Time

Inside the Makefile there is the following line:

MEASURETIME = nanoseconds

If you want to measure the execution time by nanoseconds, keep this code as shown. If you want to measure the cycles count, then modify it to

MEASURETIME = cycles

Then again, clean and make with

make clean
make
./test

Note

The included Makefile does not have any -O2 nor -O3 flag. If you want to optimize, then add -O2 (or -O3) into the line

$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(SOURCES) -g $(EXTRACONDITIONS) -lssl -lcrypto -D $(MEASURETIME)

becoming

$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(SOURCES) -g $(EXTRACONDITIONS) -lssl -lcrypto -D $(MEASURETIME) -O3

In some cases, depedning on your code, architecture and optimization flags, you can get CPU counts really small (or 0). When you compile with -O3, unused sections of code and variables are skipped.

If you want to check what it is happening in the assembly, just run

objdump -d test > test_asm
sudo nano test_asm

Modifying custom code

Inside the Main.cpp, you will find the following code

unsigned long long startTime = 0;
unsigned long long endTime = 0;
unsigned long long totalTime = 0;

startTime = get_timestamp();

//Do something. This code is just an example
for (int i = 0; i < 99999; i++) {
  int temp = (int)(i * i * i * i);
}

endTime = get_timestamp();

unsigned long long executionTime = ((unsigned long long)(endTime - startTime));
totalTime += executionTime;

As you can see, to measure the time (either in nanoseconds or CPU cycles), just add

startTime = get_timestamp();

before your code, and

endTime = get_timestamp();

after your code. Then deduct the difference by

unsigned long long executionTime = ((unsigned long long)(endTime - startTime));

and add it to your global execution time variable as

totalTime += executionTime;

Limitations

Originally this code only worked for Cortex A-72 CPUs. Now it works for Cortex A-72 and Intel CPUs, with the limitation that for Intel CPUs only the execution time (in nanoseconds) will be measured.

Warnings

If you get an Illegal instruction error, its because you are trying to measure the CPU cycles without mounting the Kernel module. Just run

cd enable_ccr
make
make install