1#!/usr/bin/env bcc-lua
2--[[
3Copyright 2016 Marek Vavrusa <mvavrusa@cloudflare.com>
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-- This example program measures latency of block device operations and plots it
18-- in a histogram. It is similar to BPF example:
19-- https://github.com/torvalds/linux/blob/master/samples/bpf/tracex3_kern.c
20local ffi = require('ffi')
21local bpf = require('bpf')
22local S = require('syscall')
23
24-- Shared part of the program
25local bins = 100
26local map = bpf.map('hash', 512, ffi.typeof('uint64_t'), ffi.typeof('uint64_t'))
27local lat_map = bpf.map('array', bins)
28
29-- Kernel-space part of the program
30local trace_start = bpf.kprobe('myprobe:blk_start_request', function (ptregs)
31	map[ptregs.parm1] = time()
32end, false, -1, 0)
33local trace_end = bpf.kprobe('myprobe2:blk_account_io_completion', function (ptregs)
34	-- The lines below are computing index
35	-- using log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
36	-- index = 29 ~ 1 usec
37	-- index = 59 ~ 1 msec
38	-- index = 89 ~ 1 sec
39	-- index = 99 ~ 10sec or more
40	local delta = time() - map[ptregs.parm1]
41	local index = 3 * math.log2(delta)
42	if index >= bins then
43		index = bins-1
44	end
45	xadd(lat_map[index], 1)
46	return true
47end, false, -1, 0)
48-- User-space part of the program
49pcall(function()
50	local counter = 0
51	local sym = {' ',' ','.','.','*','*','o','o','O','O','#','#'}
52	while true do
53		-- Print header once in a while
54		if counter % 50 == 0 then
55			print('|1us      |10us     |100us    |1ms      |10ms     |100ms    |1s       |10s')
56			counter = 0
57		end
58		counter = counter + 1
59		-- Collect all events
60		local hist, events = {}, 0
61		for i=29,bins-1 do
62			local v = tonumber(lat_map[i] or 0)
63			if v > 0 then
64				hist[i] = hist[i] or 0 + v
65				events = events + v
66			end
67		end
68		-- Print histogram symbols based on relative frequency
69		local s = ''
70		for i=29,bins-1 do
71			if hist[i] then
72				local c = math.ceil((hist[i] / (events + 1)) * #sym)
73				s = s .. sym[c]
74			else s = s .. ' ' end
75		end
76		print(s .. string.format('  ; %d events', events))
77		S.sleep(1)
78	end
79end)