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
12 struct start_key {
13 dev_t dev;
14 u32 _pad;
15 sector_t sector;
16 };
17
18 struct {
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 */
26 SEC("tracepoint/block/block_io_start")
bpf_prog1(struct trace_event_raw_block_rq * ctx)27 int 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
log2l(unsigned long long n)39 static 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
50 struct {
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 */
58 SEC("tracepoint/block/block_io_done")
bpf_prog2(struct trace_event_raw_block_rq * ctx)59 int 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 }
99 char _license[] SEC("license") = "GPL";
100 u32 _version SEC("version") = LINUX_VERSION_CODE;
101
