Re: Stap scripts to track task cpu changes

[William Cohen <wcohen at redhat dot com>]

Ankita Garg wrote:
> 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.

I would like to add these example to the systemtap examples. I have looked
through them and made some tweaks. For both of them I formatted them not to use
tabs so they can used in documentation.

For chng_cpu.stp use the appropriate probe point, scheduler.cpu_on.  Why the
check for "tid() != 0"?

For migrate.stp The check "$1 != 0" seemed to be unneeded. Was there a reason
for using $p->pid and kernel_string($p->comm) rather tid() and execname()?  The
test is using "tid() == $1"

-Will



/*    Filename: chng_cpu.stp
 *      Author: Ankita Garg <ankita@in.ibm.com>
 * Description: Captures information on the number of times an executable
 * 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 (C) IBM Corp. 2009.  All Rights Reserved.
 *
 */

global threads

probe scheduler.cpu_on
{
  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();
}

/*    Filename: migrate.stp
 *      Author: Ankita Garg <ankita@in.ibm.com>
 * Description: Captures information on the migration of a thread
 *
 * 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 (C) IBM Corp. 2009.  All Rights Reserved.
 *
*/

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