1#!/usr/bin/env bcc-lua
2--[[
3Copyright 2016 GitHub, Inc
4
5Licensed under the Apache License, Version 2.0 (the "License");
6you may not use this file except in compliance with the License.
7You may obtain a copy of the License at
8
9http://www.apache.org/licenses/LICENSE-2.0
10
11Unless required by applicable law or agreed to in writing, software
12distributed under the License is distributed on an "AS IS" BASIS,
13WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14See the License for the specific language governing permissions and
15limitations under the License.
16]]
17
18local program = [[
19#include <uapi/linux/ptrace.h>
20#include <linux/sched.h>
21
22struct key_t {
23  u32 prev_pid;
24  u32 curr_pid;
25};
26// map_type, key_type, leaf_type, table_name, num_entry
27BPF_HASH(stats, struct key_t, u64, 1024);
28int count_sched(struct pt_regs *ctx, struct task_struct *prev) {
29  struct key_t key = {};
30  u64 zero = 0, *val;
31
32  key.curr_pid = bpf_get_current_pid_tgid();
33  key.prev_pid = prev->pid;
34
35  val = stats.lookup_or_init(&key, &zero);
36  (*val)++;
37  return 0;
38}
39]]
40
41return function(BPF)
42  local b = BPF:new{text=program, debug=0}
43  b:attach_kprobe{event="finish_task_switch", fn_name="count_sched"}
44
45  print("Press any key...")
46  io.read()
47
48  local t = b:get_table("stats")
49  for k, v in t:items() do
50    print("task_switch[%d -> %d] = %d" % {k.prev_pid, k.curr_pid, tonumber(v)})
51  end
52end
53