Stap scripts to track task cpu changes

[Ankita Garg <ankita at in dot ibm dot com>]

Hello folks,

Quite sometime back, I was faced with a situation where I needed to
track instances when a particular task was being migrated away from a
cpu. I used the following trivial script. The tid needs to be passed as
parameter. Sharing it, hoping it might be useful for some folks.

/*    Filename: migrate.stp
 *      Author: Ankita Garg <ankita@in.ibm.com>
 * Description: Captures information on the migration of threads 
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * © Copyright IBM Corp. 2009.  All Rights Reserved.
 *
*/

probe kernel.function("__migrate_task")
{
	if(($1 != 0 ) && (tid() == $1)) {
		printf ("thread %d (%s) is migrating from %d to %d \n", $p->pid,
				kernel_string($p->comm), $src_cpu, $dest_cpu);
	}
}


Below is a script that tracks all the cpus that a particular task ran
on. Pl note it does not track the context switches.

/*    Filename: chng_cpu.stp
 *      Author: Ankita Garg <ankita@in.ibm.com>
 * Description: Captures information on the number of times java thread
 * switches cpu
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * © Copyright IBM Corp. 2009.  All Rights Reserved.
 *
*/

global threads

probe kernel.function("finish_task_switch")
{
        if ((threads[tid()] != cpu()) && (tid() != 0) && (execname() == @1)) {
                printf("thread %d (%s) context switched on %d \n",
                                tid(), execname(), cpu());
				printf("state: %d\n", task_state(task_current()))
				print_stack(backtrace())
	}
        threads[tid()] = cpu();
}

With the new tracepoints infrastructure, the above stats could maybe be
captured in a much easier way, however, it worked well with stap as well
:-) Do let me know if you have any suggestions.


-- 
Regards,
Ankita Garg (ankita@in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs, 
Bangalore, India

Attachment: migrate.stp
Description: Text document

Attachment: chng_cpu.stp
Description: Text document