#!/usr/bin/python3
# Copyright (c) PLUMgrid, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")

from bcc import BPF
from time import sleep

b = BPF(text="""
#include <uapi/linux/ptrace.h>
#include <linux/sched.h>

struct key_t {
  u32 prev_pid;
  u32 curr_pid;
};
// map_type, key_type, leaf_type, table_name, num_entry
BPF_HASH(stats, struct key_t, u64, 1024);
int count_sched(struct pt_regs *ctx, struct task_struct *prev) {
  struct key_t key = {};
  u64 zero = 0, *val;

  key.curr_pid = bpf_get_current_pid_tgid();
  key.prev_pid = prev->pid;

  // could also use `stats.increment(key);`
  val = stats.lookup_or_init(&key, &zero);
  (*val)++;
  return 0;
}
""")
b.attach_kprobe(event="finish_task_switch", fn_name="count_sched")

# generate many schedule events
for i in range(0, 100): sleep(0.01)

for k, v in b["stats"].items():
    print("task_switch[%5d->%5d]=%u" % (k.prev_pid, k.curr_pid, v.value))