前言
当我们很多时候在分析定位一个比较隐秘的问题时，我们马上能脱口而出好几种方法，查日志找异常，再细致一点的，jmap，jstack分析stack trace。但是一般如果到了分析stack trance的阶段时，说明这个很可能已经是performance的问题了。但其实很多时候，jstack这种默认的命令工具对于开发者来说还不够直观与好理解。它所展现的只是一堆的当前stack trance的展现，没有汇聚的阶段性的调用占比。jstack的结果还需要人工进行二次分析。因此，本文笔者来聊聊在这方面比较适用的一个工具：Flame Graph（火焰图）。
什么是Flame Graph
首先我们来了解火焰图的概念，以下是比较官方的解释：
This visualization of software execution is a new necessity for performance profiling and debugging.
以上译为：一种软件执行情况的形象化的反映，用于做性能profile和debug。
以下是flame graph的一张呈现效果图
后面笔者再介绍上图的含义。
Flame Graph的工作原理
在Flame Graph在呈现出整个最终结果之前，其中主要的工作并不是图形的展现，而是前面profile数据的采集。
这里数据的采集首先按照profile的类型分为以下几类：
- CPU的profile分析，那需要进行的stack trace的采集，可以借助于Linux的perf命令
- Memory的profile，那我们需要sample一些malloc类似的系统调用。
- Off-CPU的profile，那些没有消耗CPU的线程的profile，可以理解为被block住的线程。
…
以上不同类型的profile需要依赖不同的采集工具，比较常见的还是CPU profile，对于CPU的profile，它要做的其实就是进程stack trace的收集。这个收集可以按照采集总时间，采集频率来进行。
假设我们用Linux的perf命令，对某进程id为1234的进程，进行持续60s，采集频率为每秒99次的CPU使用情况要求，命令如下：
sudo perf record -F 99 -p 1234 -g --sleep 60
上述生成的stack trace全部展现出来会相当的庞大，补过perf命令可以帮助对此进行折叠，汇总统计，然后将结果文件交由Flame Graph进行最后展示。展现效果如上小节图中所示。
上述图中，y轴高度表示的stack trace的调用深度，从上往下为从child–>parent的关系，x轴宽度表示调用的频率，所以我们在观察flame Graph的时候，要观察最顶部的那些宽度比较宽的stack信息。
Flame Graph通过图形的方式能够帮助开发者迅速定位出明显消耗资源的调用，唯一可能不足的地方在于上面每个小格子的显示空间有限，没有办法显示全操作方法名，需要再次点进去进行更一步的查看。
附：Profile的页面快速执行构建工具
最近发现有些系统代码把profile行为整合到了系统代码中，做了一个ProfileServlet，然后用户可通过页面url访问能快速得到指定进程的profile结果，相当方便，代码如下（最原始来自于Hive社区），作为和本文主题的相关内容，贴出代码，后续对大家可能有所帮助
:
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hdds.server;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.management.ManagementFactory;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import com.google.common.base.Joiner;
import org.apache.commons.io.IOUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Servlet that runs async-profiler as web-endpoint.
* <p>
* Source: https://github.com/apache/hive/blob/master/common/src/java/org
* /apache/hive/http/ProfileServlet.java
* <p>
* Following options from async-profiler can be specified as query paramater.
* // -e event profiling event: cpu|alloc|lock|cache-misses etc.
* // -d duration run profiling for <duration> seconds (integer)
* // -i interval sampling interval in nanoseconds (long)
* // -j jstackdepth maximum Java stack depth (integer)
* // -b bufsize frame buffer size (long)
* // -t profile different threads separately
* // -s simple class names instead of FQN
* // -o fmt[,fmt...] output format:
* summary|traces|flat|collapsed|svg|tree|jfr
* // --width px SVG width pixels (integer)
* // --height px SVG frame height pixels (integer)
* // --minwidth px skip frames smaller than px (double)
* // --reverse generate stack-reversed FlameGraph / Call tree
* Example:
* - To collect 30 second CPU profile of current process (returns FlameGraph
* svg)
* curl "http://localhost:10002/prof"
* - To collect 1 minute CPU profile of current process and output in tree
* format (html)
* curl "http://localhost:10002/prof?output=tree&duration=60"
* - To collect 30 second heap allocation profile of current process (returns
* FlameGraph svg)
* curl "http://localhost:10002/prof?event=alloc"
* - To collect lock contention profile of current process (returns
* FlameGraph svg)
* curl "http://localhost:10002/prof?event=lock"
* Following event types are supported (default is 'cpu') (NOTE: not all
* OS'es support all events)
* // Perf events:
* // cpu
* // page-faults
* // context-switches
* // cycles
* // instructions
* // cache-references
* // cache-misses
* // branches
* // branch-misses
* // bus-cycles
* // L1-dcache-load-misses
* // LLC-load-misses
* // dTLB-load-misses
* // mem:breakpoint
* // trace:tracepoint
* // Java events:
* // alloc
* // lock
*/
public class ProfileServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final Logger LOG =
LoggerFactory.getLogger(ProfileServlet.class);
private static final String ACCESS_CONTROL_ALLOW_METHODS =
"Access-Control-Allow-Methods";
private static final String ALLOWED_METHODS = "GET";
private static final String ACCESS_CONTROL_ALLOW_ORIGIN =
"Access-Control-Allow-Origin";
private static final String CONTENT_TYPE_TEXT = "text/plain; charset=utf-8";
private static final String ASYNC_PROFILER_HOME_ENV = "ASYNC_PROFILER_HOME";
private static final String ASYNC_PROFILER_HOME_SYSTEM_PROPERTY =
"async.profiler.home";
private static final String PROFILER_SCRIPT = "/profiler.sh";
private static final int DEFAULT_DURATION_SECONDS = 10;
private static final AtomicInteger ID_GEN = new AtomicInteger(0);
static final Path OUTPUT_DIR =
Paths.get(System.getProperty("java.io.tmpdir"), "prof-output");
private Lock profilerLock = new ReentrantLock();
private Integer pid;
private String asyncProfilerHome;
private transient Process process;
public ProfileServlet() {
this.asyncProfilerHome = getAsyncProfilerHome();
this.pid = getPid();
LOG.info("Servlet process PID: {} asyncProfilerHome: {}", pid,
asyncProfilerHome);
try {
Files.createDirectories(OUTPUT_DIR);
} catch (IOException e) {
LOG.error(
"Can't create the output directory for java profiler: " + OUTPUT_DIR,
e);
}
}
private Integer getPid() {
// JVM_PID is exported by bin/ozone
String pidStr = System.getenv("JVM_PID");
// in case if it is not set correctly used fallback from mxbean which is
// implementation specific
if (pidStr == null || pidStr.trim().isEmpty()) {
String name = ManagementFactory.getRuntimeMXBean().getName();
if (name != null) {
int idx = name.indexOf("@");
if (idx != -1) {
pidStr = name.substring(0, name.indexOf("@"));
}
}
}
try {
if (pidStr != null) {
return Integer.valueOf(pidStr);
}
} catch (NumberFormatException nfe) {
// ignore
}
return null;
}
public Process runCmdAsync(List<String> cmd) {
try {
LOG.info("Running command async: " + cmd);
return new ProcessBuilder(cmd).inheritIO().start();
} catch (IOException ex) {
throw new IllegalStateException(ex);
}
}
@Override
protected void doGet(final HttpServletRequest req,
final HttpServletResponse resp) throws IOException {
// make sure async profiler home is set
if (asyncProfilerHome == null || asyncProfilerHome.trim().isEmpty()) {
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
setResponseHeader(resp);
resp.getWriter().write("ASYNC_PROFILER_HOME env is not set.");
return;
}
//download the finished file
if (req.getParameter("file") != null) {
doGetDownload(req.getParameter("file"), req, resp);
return;
}
// if pid is explicitly specified, use it else default to current process
pid = getInteger(req, "pid", pid);
// if pid is not specified in query param and if current process pid
// cannot be determined
if (pid == null) {
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
setResponseHeader(resp);
resp.getWriter().write(
"'pid' query parameter unspecified or unable to determine PID of "
+ "current process.");
return;
}
final int duration = getInteger(req, "duration", DEFAULT_DURATION_SECONDS);
final Output output = getOutput(req);
final Event event = getEvent(req);
final Long interval = getLong(req, "interval");
final Integer jstackDepth = getInteger(req, "jstackdepth", null);
final Long bufsize = getLong(req, "bufsize");
final boolean thread = req.getParameterMap().containsKey("thread");
final boolean simple = req.getParameterMap().containsKey("simple");
final Integer width = getInteger(req, "width", null);
final Integer height = getInteger(req, "height", null);
final Double minwidth = getMinWidth(req);
final boolean reverse = req.getParameterMap().containsKey("reverse");
if (process == null || !process.isAlive()) {
try {
int lockTimeoutSecs = 3;
if (profilerLock.tryLock(lockTimeoutSecs, TimeUnit.SECONDS)) {
try {
File outputFile =
OUTPUT_DIR.resolve("async-prof-pid-" + pid + "-" +
event.name().toLowerCase() + "-" + ID_GEN.incrementAndGet()
+ "." +
output.name().toLowerCase()).toFile();
List<String> cmd = new ArrayList<>();
cmd.add(asyncProfilerHome + PROFILER_SCRIPT);
cmd.add("-e");
cmd.add(event.getInternalName());
cmd.add("-d");
cmd.add("" + duration);
cmd.add("-o");
cmd.add(output.name().toLowerCase());
cmd.add("-f");
cmd.add(outputFile.getAbsolutePath());
if (interval != null) {
cmd.add("-i");
cmd.add(interval.toString());
}
if (jstackDepth != null) {
cmd.add("-j");
cmd.add(jstackDepth.toString());
}
if (bufsize != null) {
cmd.add("-b");
cmd.add(bufsize.toString());
}
if (thread) {
cmd.add("-t");
}
if (simple) {
cmd.add("-s");
}
if (width != null) {
cmd.add("--width");
cmd.add(width.toString());
}
if (height != null) {
cmd.add("--height");
cmd.add(height.toString());
}
if (minwidth != null) {
cmd.add("--minwidth");
cmd.add(minwidth.toString());
}
if (reverse) {
cmd.add("--reverse");
}
cmd.add(pid.toString());
process = runCmdAsync(cmd);
// set response and set refresh header to output location
setResponseHeader(resp);
resp.setStatus(HttpServletResponse.SC_ACCEPTED);
String relativeUrl = "/prof?file=" + outputFile.getName();
resp.getWriter().write(
"Started [" + event.getInternalName()
+ "] profiling. This page will automatically redirect to " +
relativeUrl + " after " + duration
+ " seconds.
command:
" + Joiner.on(" ").join(cmd));
resp.getWriter().write(
"
Please make sure that you enabled the profiling on "
+ "kernel level:
"
+ "echo 1 > /proc/sys/kernel/perf_event_paranoid
"
+ "echo 0 > /proc/sys/kernel/kptr_restrict
"
+ "See https://github"
+ ".com/jvm-profiling-tools/async-profiler#basic-usage"
+ " for more details.");
// to avoid auto-refresh by ProfileOutputServlet, refreshDelay
// can be specified via url param
int refreshDelay = getInteger(req, "refreshDelay", 0);
// instead of sending redirect, set auto-refresh so that browsers
// will refresh with redirected url
resp.setHeader("Refresh",
(duration + refreshDelay) + ";" + relativeUrl);
resp.getWriter().flush();
} finally {
profilerLock.unlock();
}
} else {
setResponseHeader(resp);
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
resp.getWriter().write(
"Unable to acquire lock. Another instance of profiler might be "
+ "running.");
LOG.warn(
"Unable to acquire lock in {} seconds. Another instance of "
+ "profiler might be running.",
lockTimeoutSecs);
}
} catch (InterruptedException e) {
LOG.warn("Interrupted while acquiring profile lock.", e);
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
}
} else {
setResponseHeader(resp);
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
resp.getWriter()
.write("Another instance of profiler is already running.");
}
}
protected void doGetDownload(String fileName, final HttpServletRequest req,
final HttpServletResponse resp)
throws IOException {
File requestedFile =
ProfileServlet.OUTPUT_DIR.resolve(fileName).toAbsolutePath()
.toFile();
// async-profiler version 1.4 writes 'Started [cpu] profiling' to output
// file when profiler is running which
// gets replaced by final output. If final output is not ready yet, the
// file size will be <100 bytes (in all modes).
if (requestedFile.length() < 100) {
LOG.info("{} is incomplete. Sending auto-refresh header..",
requestedFile);
resp.setHeader("Refresh",
"2," + req.getRequestURI() + "?file=" + fileName);
resp.getWriter().write(
"This page will auto-refresh every 2 second until output file is "
+ "ready..");
} else {
if (fileName.endsWith(".svg")) {
resp.setContentType("image/svg+xml");
} else if (fileName.endsWith(".tree")) {
resp.setContentType("text/html");
}
try (InputStream input = new FileInputStream(requestedFile)) {
IOUtils.copy(input, resp.getOutputStream());
}
}
}
private Integer getInteger(final HttpServletRequest req, final String param,
final Integer defaultValue) {
final String value = req.getParameter(param);
if (value != null) {
try {
return Integer.valueOf(value);
} catch (NumberFormatException e) {
return defaultValue;
}
}
return defaultValue;
}
private Long getLong(final HttpServletRequest req, final String param) {
final String value = req.getParameter(param);
if (value != null) {
try {
return Long.valueOf(value);
} catch (NumberFormatException e) {
return null;
}
}
return null;
}
private Double getMinWidth(final HttpServletRequest req) {
final String value = req.getParameter("minwidth");
if (value != null) {
try {
return Double.valueOf(value);
} catch (NumberFormatException e) {
return null;
}
}
return null;
}
private Event getEvent(final HttpServletRequest req) {
final String eventArg = req.getParameter("event");
if (eventArg != null) {
Event event = Event.fromInternalName(eventArg);
return event == null ? Event.CPU : event;
}
return Event.CPU;
}
private Output getOutput(final HttpServletRequest req) {
final String outputArg = req.getParameter("output");
if (req.getParameter("output") != null) {
try {
return Output.valueOf(outputArg.trim().toUpperCase());
} catch (IllegalArgumentException e) {
return Output.SVG;
}
}
return Output.SVG;
}
private void setResponseHeader(final HttpServletResponse response) {
response.setHeader(ACCESS_CONTROL_ALLOW_METHODS, ALLOWED_METHODS);
response.setHeader(ACCESS_CONTROL_ALLOW_ORIGIN, "*");
response.setContentType(CONTENT_TYPE_TEXT);
}
static String getAsyncProfilerHome() {
String asyncProfilerHome = System.getenv(ASYNC_PROFILER_HOME_ENV);
// if ENV is not set, see if -Dasync.profiler
// .home=/path/to/async/profiler/home is set
if (asyncProfilerHome == null || asyncProfilerHome.trim().isEmpty()) {
asyncProfilerHome =
System.getProperty(ASYNC_PROFILER_HOME_SYSTEM_PROPERTY);
}
return asyncProfilerHome;
}
enum Event {
CPU("cpu"),
ALLOC("alloc"),
LOCK("lock"),
PAGE_FAULTS("page-faults"),
CONTEXT_SWITCHES("context-switches"),
CYCLES("cycles"),
INSTRUCTIONS("instructions"),
CACHE_REFERENCES("cache-references"),
CACHE_MISSES("cache-misses"),
BRANCHES("branches"),
BRANCH_MISSES("branch-misses"),
BUS_CYCLES("bus-cycles"),
L1_DCACHE_LOAD_MISSES("L1-dcache-load-misses"),
LLC_LOAD_MISSES("LLC-load-misses"),
DTLB_LOAD_MISSES("dTLB-load-misses"),
MEM_BREAKPOINT("mem:breakpoint"),
TRACE_TRACEPOINT("trace:tracepoint");
private String internalName;
Event(final String internalName) {
this.internalName = internalName;
}
public String getInternalName() {
return internalName;
}
public static Event fromInternalName(final String name) {
for (Event event : values()) {
if (event.getInternalName().equalsIgnoreCase(name)) {
return event;
}
}
return null;
}
}
enum Output {
SUMMARY,
TRACES,
FLAT,
COLLAPSED,
SVG,
TREE,
JFR
}
}
引用
[1].https://queue.acm.org/detail.cfm?id=2927301
[2].http://www.brendangregg.com/flamegraphs.html