1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2018 Facebook
3 
4 #include <linux/bpf.h>
5 #include <bpf/bpf_helpers.h>
6 
7 #ifndef PERF_MAX_STACK_DEPTH
8 #define PERF_MAX_STACK_DEPTH         127
9 #endif
10 
11 struct {
12 	__uint(type, BPF_MAP_TYPE_ARRAY);
13 	__uint(max_entries, 1);
14 	__type(key, __u32);
15 	__type(value, __u32);
16 } control_map SEC(".maps");
17 
18 struct {
19 	__uint(type, BPF_MAP_TYPE_HASH);
20 	__uint(max_entries, 16384);
21 	__type(key, __u32);
22 	__type(value, __u32);
23 } stackid_hmap SEC(".maps");
24 
25 typedef __u64 stack_trace_t[PERF_MAX_STACK_DEPTH];
26 
27 struct {
28 	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
29 	__uint(max_entries, 16384);
30 	__uint(key_size, sizeof(__u32));
31 	__uint(value_size, sizeof(stack_trace_t));
32 } stackmap SEC(".maps");
33 
34 struct {
35 	__uint(type, BPF_MAP_TYPE_ARRAY);
36 	__uint(max_entries, 16384);
37 	__type(key, __u32);
38 	__type(value, stack_trace_t);
39 } stack_amap SEC(".maps");
40 
41 /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
42 struct sched_switch_args {
43 	unsigned long long pad;
44 	char prev_comm[16];
45 	int prev_pid;
46 	int prev_prio;
47 	long long prev_state;
48 	char next_comm[16];
49 	int next_pid;
50 	int next_prio;
51 };
52 
53 SEC("tracepoint/sched/sched_switch")
54 int oncpu(struct sched_switch_args *ctx)
55 {
56 	__u32 max_len = PERF_MAX_STACK_DEPTH * sizeof(__u64);
57 	__u32 key = 0, val = 0, *value_p;
58 	void *stack_p;
59 
60 	value_p = bpf_map_lookup_elem(&control_map, &key);
61 	if (value_p && *value_p)
62 		return 0; /* skip if non-zero *value_p */
63 
64 	/* The size of stackmap and stackid_hmap should be the same */
65 	key = bpf_get_stackid(ctx, &stackmap, 0);
66 	if ((int)key >= 0) {
67 		bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
68 		stack_p = bpf_map_lookup_elem(&stack_amap, &key);
69 		if (stack_p)
70 			bpf_get_stack(ctx, stack_p, max_len, 0);
71 	}
72 
73 	return 0;
74 }
75 
76 char _license[] SEC("license") = "GPL";
77