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1.3 Tick Processor.md

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V8 内置了一个性能分析工具——Tick Processor,可以记录 JavaScript/C/C++ 代码的堆栈信息,该功能默认是关闭的,可以通过添加命令行参数 --prof 开启。

1.3.1 Tick Processor

创建测试代码:

app.js

const crypto = require('crypto')

function hash (password) {
  const salt = crypto.randomBytes(128).toString('base64')
  const hash = crypto.pbkdf2Sync(password, salt, 10000, 64, 'sha512')
  return hash
}

console.time('pbkdf2Sync')
for (let i = 0; i < 100; i++) {
  hash('random_password')
}
console.timeEnd('pbkdf2Sync')

运行:

$ node --prof app
pbkdf2Sync: 1375.582ms

可以看出,执行 100 次 hash 函数总共用了 1375.585ms,并且当前目录下多了一个 isolate-xxx-v8.log 文件,该文件记录了 V8 的性能日志,内容如下:

v8-version,6,1,534,50,0
shared-library,"/usr/local/bin/node",0x100001800,0x100bbb69a,0
...
code-creation,Function,18,111912,0x37d07c7246a8,144,"hash /Users/nswbmw/Desktop/test/app.js:3:15",0x37d07c7076d0,~
code-creation,LazyCompile,18,111927,0x37d07c7246a8,144,"hash /Users/nswbmw/Desktop/test/app.js:3:15",0x37d07c7076d0,~
code-creation,Function,18,112058,0x37d07c725690,80,"exports.pbkdf2Sync crypto.js:686:30",0x37d07c70cb58,~
code-creation,LazyCompile,18,112074,0x37d07c725690,80,"exports.pbkdf2Sync crypto.js:686:30",0x37d07c70cb58,~
...

早期我们需要借助 node-tick-processor 这样的工具解析 v8.log,但 Node.js 在 v5.2.0 之后包含了 v8.log 处理器,添加命令行参数 --prof-process 开启。

运行:

$ node --prof-process isolate-0x103000000-v8.log

结果如下:

Statistical profiling result from isolate-0x103000000-v8.log, (1152 ticks, 44 unaccounted, 0 excluded).

 [Shared libraries]:
   ticks  total  nonlib   name

 [JavaScript]:
   ticks  total  nonlib   name
      1    0.1%    0.1%  Function: ~Uint8Array native typedarray.js:158:31
      1    0.1%    0.1%  Function: ~NativeModule.cache bootstrap_node.js:604:42
      1    0.1%    0.1%  Function: ~Buffer.toString buffer.js:609:37

 [C++]:
   ticks  total  nonlib   name
   1023   88.8%   88.8%  T node::crypto::PBKDF2(v8::FunctionCallbackInfo<v8::Value> const&)
     27    2.3%    2.3%  t node::(anonymous namespace)::ContextifyScript::New(v8::FunctionCallbackInfo<v8::Value> const&)
     ...

 [Summary]:
   ticks  total  nonlib   name
      3    0.3%    0.3%  JavaScript
   1105   95.9%   95.9%  C++
      3    0.3%    0.3%  GC
      0    0.0%          Shared libraries
     44    3.8%          Unaccounted

 [C++ entry points]:
   ticks    cpp   total   name
   1062   98.2%   92.2%  T v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*)
     13    1.2%    1.1%  T v8::internal::Runtime_CompileLazy(int, v8::internal::Object**, v8::internal::Isolate*)
     ...

 [Bottom up (heavy) profile]:
  Note: percentage shows a share of a particular caller in the total
  amount of its parent calls.
  Callers occupying less than 1.0% are not shown.

   ticks parent  name
   1023   88.8%  T node::crypto::PBKDF2(v8::FunctionCallbackInfo<v8::Value> const&)
   1023  100.0%    T v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*)
   1023  100.0%      Function: ~pbkdf2 crypto.js:691:16
   1023  100.0%        Function: ~exports.pbkdf2Sync crypto.js:686:30
   1023  100.0%          Function: ~hash /Users/nswbmw/Desktop/test/app.js:3:15
   1023  100.0%            Function: ~<anonymous> /Users/nswbmw/Desktop/test/app.js:1:11
   ...

打印结果包含六部分:Shared libraries、JavaScript、C++、Summary、C++ entry points 和 Bottom up (heavy) profile。[JavaScript] 部分列出了 JavaScript 代码执行所占用的 CPU ticks(CPU 时钟周期),[C++] 部分列出了 C++ 代码执行所占用的 CPU ticks,[Summary] 列出了各个部分的占比,[Bottom up] 列出了所有 CPU 占用时间从大到小的函数及堆栈信息,小于 1% 的则不予显示。

可以看出:88.8%的 CPU 时间都花在了 crypto.js 文件的 pbkdf2Sync 函数上,该函数在 app.js 第 3 行被调用,即我们的 hash 函数。

解决方法:将同步的 pbkdf2Sync 改为异步的 pbkdf2。修改代码如下:

const crypto = require('crypto')

function hash (password, cb) {
  const salt = crypto.randomBytes(128).toString('base64')
  crypto.pbkdf2(password, salt, 10000, 64, 'sha512', cb)
}

let count = 0
console.time('pbkdf2')
for (let i = 0; i < 100; i++) {
  hash('random_password', () => {
    count++
    if (count === 100) {
      console.timeEnd('pbkdf2')
    }
  })
}

运行结果:

$ node --prof app
pbkdf2: 656.332ms

可以看出,程序运行了 656.332ms,相比较于之前的 1375.585ms,性能提升了 1 倍。我们继续看下 v8.log 的分析结果,运行:

$ node --prof-process isolate-0x102802400-v8.log
Statistical profiling result from isolate-0x103001a00-v8.log, (198 ticks, 19 unaccounted, 0 excluded).

 [Shared libraries]:
   ticks  total  nonlib   name

 [JavaScript]:
   ticks  total  nonlib   name
      1    0.5%    0.5%  StoreIC: A store IC from the snapshot
      1    0.5%    0.5%  Function: ~set native collection.js:149:4
      1    0.5%    0.5%  Function: ~pbkdf2 crypto.js:691:16
      1    0.5%    0.5%  Function: ~inherits util.js:962:18
      1    0.5%    0.5%  Builtin: ArrayIteratorPrototypeNext

 [C++]:
   ticks  total  nonlib   name
     83   41.9%   41.9%  T ___kdebug_trace_string
     31   15.7%   15.7%  t node::(anonymous namespace)::ContextifyScript::New(v8::FunctionCallbackInfo<v8::Value> const&)
     14    7.1%    7.1%  T ___pthread_sigmask
     ...

 [Summary]:
   ticks  total  nonlib   name
      5    2.5%    2.5%  JavaScript
    174   87.9%   87.9%  C++
      3    1.5%    1.5%  GC
      0    0.0%          Shared libraries
     19    9.6%          Unaccounted

 [C++ entry points]:
   ticks    cpp   total   name
     41   60.3%   20.7%  T v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*)
     17   25.0%    8.6%  T v8::internal::Runtime_CompileLazy(int, v8::internal::Object**, v8::internal::Isolate*)
     ...

 [Bottom up (heavy) profile]:
  Note: percentage shows a share of a particular caller in the total
  amount of its parent calls.
  Callers occupying less than 1.0% are not shown.

   ticks parent  name
     83   41.9%  T ___kdebug_trace_string

     31   15.7%  t node::(anonymous namespace)::ContextifyScript::New(v8::FunctionCallbackInfo<v8::Value> const&)
     31  100.0%    T v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*)
     31  100.0%      Function: ~runInThisContext bootstrap_node.js:495:28
     31  100.0%        Function: ~NativeModule.compile bootstrap_node.js:584:44
     31  100.0%          Function: ~NativeModule.require bootstrap_node.js:516:34
     ...

可以看出,[Bottom up] 没有很多 ticks,而且不再有 pbkdf2 这种堆栈信息。

1.3.2 Web UI

V8 还提供了一个 Web 可视化工具来查看生成的 v8 日志。首先,将代码还原到使用 pbkdf2Sync 的版本,运行:

$ node --prof app # 生成 isolate-0x103000000-v8.log
$ node --prof-process --preprocess isolate-0x103000000-v8.log > v8.json # 格式化成 JSON 文件
$ git clone https://github.com/v8/v8.git # 克隆 v8 仓库
$ open v8/tools/profview/index.html # 打开 V8 profiling log processor

点击 “选择文件”,选择刚才生成的 v8.json 文件,点击 “Bottom up” 视图,如下所示:

有以下两点需要解释:

  1. 图中的上半部分展示了 CPU 的 timeline,X 轴代表时间的流逝,Y 轴代表当前时间点不同部分占用 CPU 的比例,可以在 timeline 图表上单击左键不放,然后拖动,选择时间区间。
  2. 图中的下半部分展示了当前时间段内 CPU 占用比从大到小降序排列的函数,展开可查看堆栈信息。不同的颜色代表了不同的部分,点击任意一个函数,timeline 底部会展示该函数的执行时间分布。

1.3.3 参考链接

上一节:1.2 v8-profiler

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