Experiment methodology

1. Creating random(for obtaining different checksum results) dummy test .txt files according to given size and count

2. Creating shell script that runs given hash algorithm N times

3. Reading /proc/stat and /proc/pid/stat files at the beginning and end of the hash calculation(pid value is the process id of the shell script which executes checksum N times)

4. Calculating CPU usage of the process for the specific time interval

Calculation with proc files

1. Reading below values from /proc/pid/stat file: (# indicates the column number in the stat file)

• Utime (#14): Amount of time that this process has been scheduled in user mode, measured in clock ticks
• Stime (#15): Amount of time that this process has been scheduled in kernel mode, measured in clock ticks
• Cutime (#16): Amount of time that this process’s waited-for children have been scheduled in user mode, measured in clock ticks
• Cstime (#17): Amount of time that this process’s waited-for children have been scheduled in kernel mode, measured in clock ticks

2. Calculating process’ total cpu usage for beginning and end values:

• prev_proc_cpu_total = utime + stime + cutime + cstime
• after_proc_cpu_total = utime + stime + cutime + cstime

Note: Since shell commands(in this case hash calculation command) are executed as child process in the shell script, we have to consider to calculate the total cpu usage of the process.

3. Reading below values from the first line of /proc/stat file:

• User:Normal processes executing in user mode
• Nice:Niced processes executing in user mode
• System:Processes executing in kernel mode
• Idle:Twiddling thumbs
• Iowait:Waiting for I/O to complete
• Irq:Servicing interrupts
• Softirq:Servicing softirqs

4. Calculating total cpu usage for beginning and end values:

• prev_cpu_total = user + nice + system + idle + iowait + irq + softirq
• after_cpu_total = user + nice + system + idle + iowait + irq + softirq

5. Calculating total cpu usage of the process relative to total cpu usage:

• proc_cpu_usage = 100 * (after_proc_cpu_total – prev_proc_cpu_total) / (after_cpu_total – prev_cpu_total)

Alternative method

/usr/bin/time bash myshell.sh

Above command gives us accumulated times for process and its all child processes. Cpu usage percentage can also be extracted using this command.

Results

md5sum command

Fixed file size: 10mb

Fixed file size: 30mb

sha256sum command

Fixed file size: 10mb

Fixed file size: 30mb