1/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
2 *
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
6 */
7#include "vmlinux.h"
8#include <linux/version.h>
9#include <bpf/bpf_helpers.h>
10#include <bpf/bpf_tracing.h>
11
12struct start_key {
13	dev_t dev;
14	u32 _pad;
15	sector_t sector;
16};
17
18struct {
19	__uint(type, BPF_MAP_TYPE_HASH);
20	__type(key, long);
21	__type(value, u64);
22	__uint(max_entries, 4096);
23} my_map SEC(".maps");
24
25/* from /sys/kernel/tracing/events/block/block_io_start/format */
26SEC("tracepoint/block/block_io_start")
27int bpf_prog1(struct trace_event_raw_block_rq *ctx)
28{
29	u64 val = bpf_ktime_get_ns();
30	struct start_key key = {
31		.dev = ctx->dev,
32		.sector = ctx->sector
33	};
34
35	bpf_map_update_elem(&my_map, &key, &val, BPF_ANY);
36	return 0;
37}
38
39static unsigned int log2l(unsigned long long n)
40{
41#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }
42	int i = -(n == 0);
43	S(32); S(16); S(8); S(4); S(2); S(1);
44	return i;
45#undef S
46}
47
48#define SLOTS 100
49
50struct {
51	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
52	__uint(key_size, sizeof(u32));
53	__uint(value_size, sizeof(u64));
54	__uint(max_entries, SLOTS);
55} lat_map SEC(".maps");
56
57/* from /sys/kernel/tracing/events/block/block_io_done/format */
58SEC("tracepoint/block/block_io_done")
59int bpf_prog2(struct trace_event_raw_block_rq *ctx)
60{
61	struct start_key key = {
62		.dev = ctx->dev,
63		.sector = ctx->sector
64	};
65
66	u64 *value, l, base;
67	u32 index;
68
69	value = bpf_map_lookup_elem(&my_map, &key);
70	if (!value)
71		return 0;
72
73	u64 cur_time = bpf_ktime_get_ns();
74	u64 delta = cur_time - *value;
75
76	bpf_map_delete_elem(&my_map, &key);
77
78	/* the lines below are computing index = log10(delta)*10
79	 * using integer arithmetic
80	 * index = 29 ~ 1 usec
81	 * index = 59 ~ 1 msec
82	 * index = 89 ~ 1 sec
83	 * index = 99 ~ 10sec or more
84	 * log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
85	 */
86	l = log2l(delta);
87	base = 1ll << l;
88	index = (l * 64 + (delta - base) * 64 / base) * 3 / 64;
89
90	if (index >= SLOTS)
91		index = SLOTS - 1;
92
93	value = bpf_map_lookup_elem(&lat_map, &index);
94	if (value)
95		*value += 1;
96
97	return 0;
98}
99char _license[] SEC("license") = "GPL";
100u32 _version SEC("version") = LINUX_VERSION_CODE;
101