#!/usr/bin/env bcc-lua
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--[[
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Copyright 2016 Marek Vavrusa <mvavrusa@cloudflare.com>
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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]]
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-- This example program measures latency of block device operations and plots it
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-- in a histogram. It is similar to BPF example:
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-- https://github.com/torvalds/linux/blob/master/samples/bpf/tracex3_kern.c
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local ffi = require('ffi')
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local bpf = require('bpf')
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local S = require('syscall')
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-- Shared part of the program
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local bins = 100
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local map = bpf.map('hash', 512, ffi.typeof('uint64_t'), ffi.typeof('uint64_t'))
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local lat_map = bpf.map('array', bins)
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-- Kernel-space part of the program
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local trace_start = bpf.kprobe('myprobe:blk_start_request', function (ptregs)
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map[ptregs.parm1] = time()
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end, false, -1, 0)
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local trace_end = bpf.kprobe('myprobe2:blk_account_io_completion', function (ptregs)
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-- The lines below are computing index
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-- using log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
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-- index = 29 ~ 1 usec
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-- index = 59 ~ 1 msec
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-- index = 89 ~ 1 sec
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-- index = 99 ~ 10sec or more
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local delta = time() - map[ptregs.parm1]
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local index = 3 * math.log2(delta)
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if index >= bins then
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index = bins-1
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end
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xadd(lat_map[index], 1)
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return true
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end, false, -1, 0)
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-- User-space part of the program
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pcall(function()
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local counter = 0
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local sym = {' ',' ','.','.','*','*','o','o','O','O','#','#'}
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while true do
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-- Print header once in a while
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if counter % 50 == 0 then
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print('|1us |10us |100us |1ms |10ms |100ms |1s |10s')
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counter = 0
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end
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counter = counter + 1
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-- Collect all events
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local hist, events = {}, 0
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for i=29,bins-1 do
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local v = tonumber(lat_map[i] or 0)
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if v > 0 then
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hist[i] = hist[i] or 0 + v
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events = events + v
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end
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end
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-- Print histogram symbols based on relative frequency
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local s = ''
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for i=29,bins-1 do
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if hist[i] then
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local c = math.ceil((hist[i] / (events + 1)) * #sym)
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s = s .. sym[c]
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else s = s .. ' ' end
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end
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print(s .. string.format(' ; %d events', events))
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S.sleep(1)
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end
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end)
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