free_timer.c

 1// SPDX-License-Identifier: GPL-2.0
 2/* Copyright (C) 2025. Huawei Technologies Co., Ltd */
 3#include <linux/bpf.h>
 4#include <time.h>
 5#include <bpf/bpf_tracing.h>
 6#include <bpf/bpf_helpers.h>
 7
 8#define MAX_ENTRIES 8
 9
10struct map_value {
11	struct bpf_timer timer;
12};
13
14struct {
15	__uint(type, BPF_MAP_TYPE_HASH);
16	__type(key, int);
17	__type(value, struct map_value);
18	__uint(max_entries, MAX_ENTRIES);
19} map SEC(".maps");
20
21static int timer_cb(void *map, void *key, struct map_value *value)
22{
23	volatile int sum = 0;
24	int i;
25
26	bpf_for(i, 0, 1024 * 1024) sum += i;
27
28	return 0;
29}
30
31static int start_cb(int key)
32{
33	struct map_value *value;
34
35	value = bpf_map_lookup_elem(&map, (void *)&key);
36	if (!value)
37		return 0;
38
39	bpf_timer_init(&value->timer, &map, CLOCK_MONOTONIC);
40	bpf_timer_set_callback(&value->timer, timer_cb);
41	/* Hope 100us will be enough to wake-up and run the overwrite thread */
42	bpf_timer_start(&value->timer, 100000, BPF_F_TIMER_CPU_PIN);
43
44	return 0;
45}
46
47static int overwrite_cb(int key)
48{
49	struct map_value zero = {};
50
51	/* Free the timer which may run on other CPU */
52	bpf_map_update_elem(&map, (void *)&key, &zero, BPF_ANY);
53
54	return 0;
55}
56
57SEC("syscall")
58int BPF_PROG(start_timer)
59{
60	bpf_loop(MAX_ENTRIES, start_cb, NULL, 0);
61	return 0;
62}
63
64SEC("syscall")
65int BPF_PROG(overwrite_timer)
66{
67	bpf_loop(MAX_ENTRIES, overwrite_cb, NULL, 0);
68	return 0;
69}
70
71char _license[] SEC("license") = "GPL";