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

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

2. /kernel/fork.c

line#1622

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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

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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

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+	/*
+	 * 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

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

line #2949

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

5. Compile

Results

1.Test Code

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

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gcc block.c -o block
./block

2.Find the process id

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ps -e | grep block

3.Observe the counter

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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

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kill [PID]

To be prepared to make changes to the kernel, it’s necessary to give it a try to compile the linux kernel successfully.

Environment

• VMware Fusion 7
• Ubuntu 12.04.5
• Root permission

Objective

Initially, the kernel version of the Ubuntu 12.04.5 is 3.13.0-32-generic according to

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uname -r

If you wanna check your ubuntu version, use

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cat /etc/issue

Our goal is to update the version of kernel to newer one, in this case, 3.18.

Compile the Linux Kernel

1. Download the kernel from here.

2. Copy to a directory and extract.

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cp linux-3.X.X.tar.xz /usr/src
cd /usr/src
xz -d linux-3.X.X.tar.xz
tar -xf linux-3.X.X.tar
cd linux-3.X.X

3. If not the first time to compile

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make clean
make mrproper

4. Configuration

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make menuconfig

There might be a tiny prob here saying

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fatal error: curses.h: No such file or directory

Solution under Ubuntu:

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sudo apt-get install libncurses5-dev libncursesw5-dev

5. Compile

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make
make modules_install
make install

Suggestion here: enlarge the memory size of your virtual system, which may help reduce the compiling time dramatically.

It takes hours to compile with 1 core and 1-GB memory with GUI turned on…

6. Update GRUB

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cd /boot
mkinitramfs 3.18.8 -o initrd.img-3.18.8
cp /usr/src/linux-3.18.8/arch/x86_64/boot/bzImage /boot/vmlinuz-3.18.8
ln -s /boot/System.map-3.18.8 /boot/System.map
sudo update-grub2

7. Reboot and Check!