Add Schedule Counter in Kernel

Objective

Add a feature to the linux kernel, which records the total times a process is scheduled to be executed on CPU.

Basic Idea

Add a counter varible to the struct task_struct, init the counter varible to 0 when a process is created/forked. Every time the process is scheduled to be executed, increase the counter and write the number to a proc file.

Details of how to modify the kernel

0. Environment

• VMware Fusion 7
• Ubuntu 12.04.5
• Kernel Version 3.18.8

1. /include/linux/sched.h

line#1234

struct task_struct{
+	unsigned long ctx;
	...
}

2. /kernel/fork.c

line#1622

long do_fork(unsigned long clone_flags,
      unsigned long stack_start,
      unsigned long stack_size,
      int __user *parent_tidptr,
      int __user *child_tidptr){
	  
	  	...
	  
	  	p = copy_process(clone_flags, stack_start, stack_size,
		 child_tidptr, NULL, trace);

	+	p->ctx = 0;
	
	  	...
	  
	  }

3. /kernel/sched/core.c

line#2864

asmlinkage __visible void __sched schedule(void)
{
	struct task_struct *tsk = current;

+	tsk->ctx = tsk->ctx + 1;

	sched_submit_work(tsk);
	__schedule();
}

4. /fs/proc/base.c

line #319

+	/*
+	 * Provides /proc/PID/ctx
+	 */
+	static int proc_pid_ctx(struct seq_file *m, struct pid_namespace *ns,
+				      struct pid *pid, struct task_struct *task)
+	{
+		return seq_printf(m, "%llu\n", (unsigned long long)task->ctx);
+	}

line #2603

+	ONE("ctx",  S_IRUGO, proc_pid_ctx),

line #2949

+	ONE("ctx",  S_IRUGO, proc_pid_ctx),

5. Compile

Results

1.Test Code

// block.c
#include <stdio.h>
int main(){
	while(1) getchar();
	return 0;
}

gcc block.c -o block
./block

2.Find the process id

ps -e | grep block

3.Observe the counter

cd /proc/[PID]
cat ctx

4.Increse the counter

Type anything to the block process to make it scheduled to be executed and check the content of ctx file again.

5.End

kill [PID]