Re: runtime libraries application on schedule()

[Martin Hunt <hunt at redhat dot com>]

> Use a jprobe to instrument the entry to schedule().
> Record the pid and the return address.

pid is easy.  I don't know of a way to get the return address.
I assume some inline assembly to get ebp or rbp would do it.  Something
else to add to the runtime library.

> The information could be analyzed in a sevral different ways:
> 
> 1) sum based on return address to find out which schedule points are 
> getting hit all the time
> 2) sum the counts by pid to figure out which pids are getting 
> rescheduled a lot

That's easy enough.

asmlinkage void __sched inst_schedule(void)
{
  _stp_map_key_long (schedpid, current->pid);
  _stp_map_set_int64 (schedpid, _stp_map_get_int64(schedstr) + 1);

  jprobe_return();
}

I'll attach full source to a working probe.

> 3) find out pid hitting which schedule() points
> 4) find out schedule() point being encountered by which process

I don't understand what you mean by these.  What is a schedule point?

Martin

#define HASH_TABLE_BITS 8
#define HASH_TABLE_SIZE (1<<HASH_TABLE_BITS)
#define BUCKETS 16 /* largest histogram width */
#include "../../runtime.h"

#include "../../io.c"
#include "../../map.c"


MODULE_PARM_DESC(stp, "\n");

MAP schedpid, schedstr;

asmlinkage void __sched inst_schedule(void)
{
  _stp_map_key_str (schedstr, current->comm);
  _stp_map_key_long (schedpid, current->pid);
  _stp_map_set_int64 (schedstr, _stp_map_get_int64(schedpid) + 1);
  _stp_map_set_int64 (schedpid, _stp_map_get_int64(schedstr) + 1);

  jprobe_return();
  return;
}

static struct jprobe stp_probes[] = {
  {
    .kp.addr = (kprobe_opcode_t *)0xc0309408,
    .entry = (kprobe_opcode_t *) inst_schedule
  },
};

#define MAX_STP_ROUTINE (sizeof(stp_probes)/sizeof(struct jprobe))

static int init_stp(void)
{
  int i;
  
  schedpid = _stp_map_new (10000, INT64);
  schedstr = _stp_map_new (10000, INT64);

  for (i = 0; i < MAX_STP_ROUTINE; i++) {
    dlog("plant jprobe at %p, handler addr %p\n",
	   stp_probes[i].kp.addr, stp_probes[i].entry);
    register_jprobe(&stp_probes[i]);
  }
  dlog("instrumentation is enabled...\n");
  return 0;
}

static void cleanup_stp(void)
{
  int i;
  struct map_node_int64 *ptr;

  for (i = 0; i < MAX_STP_ROUTINE; i++)
    unregister_jprobe(&stp_probes[i]);

  foreach (schedpid, ptr)
    dlog ("pid %ld = %lld\n", key1int(ptr), ptr->val); 
  dlog ("\n");

  foreach (schedstr, ptr)
    dlog ("process %s = %lld\n", key1str(ptr), ptr->val); 
  dlog ("\n");


  _stp_map_del (schedpid);
  _stp_map_del (schedstr);

  dlog("EXIT\n");
}

module_init(init_stp);
module_exit(cleanup_stp);
MODULE_LICENSE("GPL");