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diff --git a/perf_opt/con_perf.png b/perf_opt/con_perf.png
new file mode 100644
index 0000000..4073e76
Binary files /dev/null and b/perf_opt/con_perf.png differ
diff --git a/perf_opt/index.adoc b/perf_opt/index.adoc
index 6bb06e5..203c920 100644
--- a/perf_opt/index.adoc
+++ b/perf_opt/index.adoc
@@ -23,7 +23,7 @@ The builtin Go CPU profiler uses the setitimer(2) system call to ask the operati
Since Go uses non-blocking I/O, Goroutines that wait on I/O are parked and not running on any threads. Therefore they end up being largely invisible to Go's builtin CPU profiler.
____
-每秒被唤醒 100 次，记录每个线程上的栈。
+每秒被唤醒 100 次，记录每个线程上的栈，那些等待 IO 被 gopark 之类挂起的 goroutine 不会被采集到，因为不在线程上运行，gopark 挂起 goroutine 后，当前线程一般会进 schedule -> findrunnable 的调度循环。
=== fgprof
@@ -36,15 +36,41 @@ ____
可以用来诊断 CPU、IO 混合的执行时间占比。
+这个成本还是比普通的 pprof 高一些的。
+
=== trace
一般用来诊断一些诡异的抖动问题，或 runtime 的 bug(或者用来学习 runtime 的执行流)，用来做问题诊断效果一般。
基本原理是在 runtime 中埋了大量点，记录一堆 event 来追踪 runtime 执行流程。
+如果对一些调度问题有疑问，可以在 trace 里做观察，不过拿来定位问题还是比较费劲的。
+
+https://xargin.com/a-rlock-story/
+
=== perf
-perf 也是可以用的。
+perf 也是可以用的，比如线上没开 pprof 的时候，发现 CPU 炸了，perf 可以看看到底在干啥，因为 Go 默认会把 DWARF 调试信息带进二进制文件中，通过 perf 的 zoom 功能也可以一直看到哪行代码(或者是汇编)占用了比较高的 CPU。
+
+[source, text]
+----
+$ perf stat -e task-clock,cycles,instructions,cache-references,cache-misses ./hello
+yyyy
+
+ Performance counter stats for './hello':
+
+ 1.464376 task-clock (msec) # 0.979 CPUs utilized
+ 3,681,288 cycles # 2.514 GHz
+ 1,722,170 instructions # 0.47 insn per cycle
+ 46,475 cache-references # 31.737 M/sec
+ 21,479 cache-misses # 46.216 % of all cache refs
+
+ 0.001495925 seconds time elapsed
+----
+
+perf top
+
+image::perf.png[]
== 局部优化
@@ -131,6 +157,46 @@ TODO
显而易见，O(logn) 和 O(n)，O(logn) 最多就 64 次，而 O(n) 可能耗尽计算资源。
+runtime 里的算法优化：
+
+```
+ ┌──────────────────────┐
+ │ │
+ │ │
+ │ npagesKey: 130 │
+ │ spanKey: 0x1234567 │
+ │ priority: 1 │
+ │ │
+ │ │
+ └──────────────────────┘
+ │
+ ┌────────────────────┴──────────────────┐
+ │ │
+ ▼ ▼
+┌──────────────────────┐ ┌──────────────────────┐
+│ │ │ │
+│ │ │ │
+│ npagesKey: 129 │ │ npagesKey: 132 │
+│ spanKey: 0x4231560 │ │ spanKey: 0x2234521 │
+│ priority: 10 │ │ priority: 12 │
+│ │ │ │
+│ │ │ │
+└──────────────────────┘ └──────────────────────┘
+ │
+ ┌───────────┴───────────────────┐
+ │ │
+ ▼ ▼
+ ┌──────────────────────┐ ┌──────────────────────┐
+ │ │ │ │
+ │ │ │ │
+ │ npagesKey: 132 │ │ npagesKey: 136 │
+ │ spanKey: 0x2234000 │ │ spanKey: 0x2314213 │
+ │ priority: 14 │ │ priority: 131 │
+ │ │ │ │
+ │ │ │ │
+ └──────────────────────┘ └──────────────────────┘
+```
+
=== 过多的系统调用
合并调用，writev？
@@ -153,6 +219,14 @@ struct 可以复用，slice 可以复用，但 map 不太好复用。
如果数据不可变，只作查询，也可以考虑 offheap，但局限性较大。
+下面三个库可以看看。
+
+https://github.com/glycerine/offheap
+
+https://github.com/coocood/freecache
+
+https://github.com/allegro/bigcache
+
==== 减少变量逃逸
使用 go build -gcflags="-m -m" 来分析逃逸。
@@ -181,14 +255,16 @@ https://github.com/valyala/fasthttp/blob/master/workerpool.go#L19
有些开源库设计是一个 struct 对应一个 sync.Pool，这种时候，如果你不对该 struct 进行复用，就会触发 runtime 中的锁冲突：
-TODO
+参考本文中的第一个案例：
+
+https://xargin.com/lock-contention-in-go/
==== 解决方案
-* map -> sync.Map。
-* 换用无锁结构。
+* map -> sync.Map
+* 换用无锁结构，如 lock free queue、stack 等
* 分段锁
-* copy on write
+* copy on write，业务逻辑允许的前提下，在修改时拷贝一份，再修改
=== 程序局部性
@@ -197,15 +273,15 @@ TODO
时间局部性、空间局部性
[source, go]
-====
+----
var semtable [semTabSize]struct {
root semaRoot
pad [cpu.CacheLinePadSize - unsafe.Sizeof(semaRoot{})]byte
}
-====
+----
[source, go]
-====
+----
var timers [timersLen]struct {
timersBucket
@@ -213,19 +289,19 @@ var timers [timersLen]struct {
// between timersBucket values.
pad [cpu.CacheLinePadSize - unsafe.Sizeof(timersBucket{})%cpu.CacheLinePadSize]byte
}
-====
+----
类似下面的二维数组，怎么遍历更快？
[source, go]
-====
+----
var a = [10000][10000]int{}
-====
+----
在标准库中，考虑到局部性而实现的 sort 的例子：
[source, go]
-====
+----
func quickSort_func(data lessSwap, a, b, maxDepth int) {
for b-a > 12 {
if maxDepth == 0 {
@@ -251,7 +327,7 @@ func quickSort_func(data lessSwap, a, b, maxDepth int) {
insertionSort_func(data, a, b)
}
}
-====
+----
==== true sharing
@@ -264,9 +340,9 @@ ____
=== timer 性能问题
-* 老版本的 timer 会有大量的 syscall -> https://github.com/golang/go/issues/25471
+* 老版本的 timer 会有高压力下触发不准时问题，且触发大量的 syscall -> https://github.com/golang/go/issues/25471
[source, text]
-====
+----
// xiaorui.cc
go1.13
@@ -286,12 +362,16 @@ go1.14
11.55 0.950730 44 21569 epoll_pwait
9.75 0.802715 36 22181 sched_yield:w
-====
+----
+
+优化后，CPU 占用降低，到时不触发的问题也有所改善。
* 用时间轮实现粗粒度的时间库
可以搜搜大量的 timewheel 库。
+ticker 使用时要尤其注意泄露问题，否则程序 CPU 使用会逐渐上涨。
+
=== 汇编优化
SIMD 优化，如 math 库。gonum 中也有一些例子。
@@ -315,7 +395,7 @@ GC 需要抢占所有 goroutine，老版本的抢占需要用户协程在 morest
=== 物理机负载高时，延迟非线性增长
-TODO
+压力高会导致响应慢，响应慢会导致并发执行的 goroutine 数变多，响应结束后的垃圾变多，同时会导致更高的调度成本和 GC 扫描成本，级联恶化。
=== 调度导致 CPU 密集型业务超时
@@ -329,6 +409,10 @@ TODO，bcrypt 的例子
导致在每一轮 GC 后都有延迟抖动，升级 1.13 后长尾请求有改善。
+sync.Pool 的设计思路：尽量从本地拿到 cache 对象，拿不到通过无锁 shared 队列去找，还是找不到，全局 lock 找或者生成新的。
+
+这种思路比较类似 L1 -> L2 -> L3 的多级缓存设计，runtime 的内存分配演进也是类似的思路。
+
=== 当前问题定位工具的局限性
难以定位抖动问题。
@@ -341,4 +425,10 @@ TODO，bcrypt 的例子
==== continuous profiling
-早发现，早治疗。
+在生产环境对更细粒度的程序性能做实时监控，方便及时发现、定位、分析问题。
+
+早发现，早治疗，晚发现，成本高。
+
+https://storage.googleapis.com/pub-tools-public-publication-data/pdf/36575.pdf
+
+image::con_perf.png[]
diff --git a/perf_opt/index.html b/perf_opt/index.html
index b95389e..be2a45d 100644
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-<div id="header">
-<h1>Go 语言性能优化</h1>
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-<p>Latency numbers every programmer should know:</p>
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-<p><a href="https://colin-scott.github.io/personal_website/research/interactive_latency.html" class="bare">https://colin-scott.github.io/personal_website/research/interactive_latency.html</a></p>
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-<h2 id="true优化工作流"><a class="anchor" href="#true优化工作流"></a>优化工作流</h2>
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-<p>建立评估指标(eg. Latency) → 提出解决方案 → 尝试方案</p>
-</div>
-<div class="paragraph">
-<p>不断重复</p>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="true问题定位工具"><a class="anchor" href="#true问题定位工具"></a>问题定位工具</h2>
-<div class="sectionbody">
-<div class="sect2">
-<h3 id="truepprof"><a class="anchor" href="#truepprof"></a>pprof</h3>
-<div class="paragraph">
-<p>基本原理：</p>
-</div>
-<div class="quoteblock">
-<blockquote>
-<div class="paragraph">
-<p>The builtin Go CPU profiler uses the setitimer(2) system call to ask the operating system to be sent a SIGPROF signal 100 times a second. Each signal stops the Go process and gets delivered to a random thread’s sigtrampgo() function. This function then proceeds to call sigprof() or sigprofNonGo() to record the thread’s current stack.</p>
-</div>
-<div class="paragraph">
-<p>Since Go uses non-blocking I/O, Goroutines that wait on I/O are parked and not running on any threads. Therefore they end up being largely invisible to Go’s builtin CPU profiler.</p>
-</div>
-</blockquote>
-</div>
-<div class="paragraph">
-<p>每秒被唤醒 100 次，记录每个线程上的栈。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="truefgprof"><a class="anchor" href="#truefgprof"></a>fgprof</h3>
-<div class="quoteblock">
-<blockquote>
-<div class="paragraph">
-<p>fgprof is implemented as a background goroutine that wakes up 99 times per second and calls runtime.GoroutineProfile. This returns a list of all goroutines regardless of their current On/Off CPU scheduling status and their call stacks.</p>
-</div>
-</blockquote>
-</div>
-<div class="paragraph">
-<p>比较类似，但是会包含那些 Off CPU 的 goroutine。</p>
-</div>
-<div class="paragraph">
-<p>可以用来诊断 CPU、IO 混合的执行时间占比。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="truetrace"><a class="anchor" href="#truetrace"></a>trace</h3>
-<div class="paragraph">
-<p>一般用来诊断一些诡异的抖动问题，或 runtime 的 bug(或者用来学习 runtime 的执行流)，用来做问题诊断效果一般。</p>
-</div>
-<div class="paragraph">
-<p>基本原理是在 runtime 中埋了大量点，记录一堆 event 来追踪 runtime 执行流程。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="trueperf"><a class="anchor" href="#trueperf"></a>perf</h3>
-<div class="paragraph">
-<p>perf 也是可以用的。</p>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="true局部优化"><a class="anchor" href="#true局部优化"></a>局部优化</h2>
-<div class="sectionbody">
-<div class="admonitionblock warning">
-<table>
-<tr>
-<td class="icon">
-<i class="fa icon-warning" title="Warning"></i>
-</td>
-<td class="content">
-<div class="paragraph">
-<p>调用外部命令</p>
-</div>
-</td>
-</tr>
-</table>
-</div>
-<div class="listingblock">
-<div class="content">
-<pre class="highlightjs highlight"><code data-lang="go" class="language-go hljs">package main
-
-import (
- "os/exec"
- "testing"
-
- uuid "github.com/satori/go.uuid"
-)
-
-var uu []byte
-var u1 uuid.UUID
-
-func BenchmarkUUIDExec(b *testing.B) {
- for i := 0; i < b.N; i++ {
- uu, _ = exec.Command("uuidgen").Output()
- }
-}
-
-func BenchmarkUUIDLib(b *testing.B) {
- for i := 0; i < b.N; i++ {
- u1 = uuid.NewV4()
- }
-}</code></pre>
-</div>
-</div>
-<div class="admonitionblock warning">
-<table>
-<tr>
-<td class="icon">
-<i class="fa icon-warning" title="Warning"></i>
-</td>
-<td class="content">
-<div class="paragraph">
-<p>字符串操作</p>
-</div>
-</td>
-</tr>
-</table>
-</div>
-<div class="paragraph">
-<p>用加号连接，和 Sprintf 差别还是比较大的：</p>
-</div>
-<div class="listingblock">
-<div class="content">
-<pre class="highlightjs highlight"><code data-lang="go" class="language-go hljs">func BenchmarkBytesBufferAppend(b *testing.B) {
- for i := 0; i < b.N; i++ {
- var msg bytes.Buffer
- msg.WriteString("userid : " + "1")
- msg.WriteString("location : " + "ab")
- }
-}
-
-func BenchmarkBytesBufferAppendSprintf(b *testing.B) {
- for i := 0; i < b.N; i++ {
- var msg bytes.Buffer
- msg.WriteString(fmt.Sprintf("userid : %d", 1))
- msg.WriteString(fmt.Sprintf("location : %s", "ab"))
- }
-}</code></pre>
-</div>
-</div>
-<div class="imageblock">
-<div class="content">
-<img src="string_bench.png" alt="string bench">
-</div>
-</div>
-<div class="paragraph">
-<p>fmt.打印系列大部分会造成变量逃逸(interface 参数)。</p>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="true全局优化"><a class="anchor" href="#true全局优化"></a>全局优化</h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>寻找程序的整体瓶颈。</p>
-</div>
-<div class="paragraph">
-<p>wrk、pprof、压测平台</p>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="true性能瓶颈举例"><a class="anchor" href="#true性能瓶颈举例"></a>性能瓶颈举例</h2>
-<div class="sectionbody">
-<div class="sect2">
-<h3 id="true业务逻辑"><a class="anchor" href="#true业务逻辑"></a>业务逻辑</h3>
-<div class="ulist">
-<ul>
-<li>
-<p>查数据库本来 in 查询就可以了，但是却 for 循环查。
-TODO</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true序列化-cpu-占用过高"><a class="anchor" href="#true序列化-cpu-占用过高"></a>序列化 CPU 占用过高</h3>
-<div class="paragraph">
-<p>寻找一些针对性进行过优化的库，或者从文本协议更换为二进制协议。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true算法时间复杂度"><a class="anchor" href="#true算法时间复杂度"></a>算法时间复杂度</h3>
-<div class="paragraph">
-<p>显而易见，O(logn) 和 O(n)，O(logn) 最多就 64 次，而 O(n) 可能耗尽计算资源。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true过多的系统调用"><a class="anchor" href="#true过多的系统调用"></a>过多的系统调用</h3>
-<div class="paragraph">
-<p>合并调用，writev？</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true过多的对象"><a class="anchor" href="#true过多的对象"></a>过多的对象</h3>
-<div class="sect3">
-<h4 id="truesync-pool"><a class="anchor" href="#truesync-pool"></a>sync.Pool</h4>
-<div class="paragraph">
-<p>sync.Pool 才能实现 zero garbage。benchmark 中的 0 alloc，其实是因为对象有复用，alloc 平均 < 1。</p>
-</div>
-<div class="paragraph">
-<p>struct 可以复用，slice 可以复用，但 map 不太好复用。</p>
-</div>
-<div class="paragraph">
-<p>复用本身可能导致 bug，例如：</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>拿出时不 Reset</p>
-</li>
-<li>
-<p>slice 缩容时，被缩掉对象如果不置 nil，是不会释放的</p>
-</li>
-<li>
-<p>在 Put 回 Pool 时，不判断大小，导致了进程占内存越来越大</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect3">
-<h4 id="trueoffheap"><a class="anchor" href="#trueoffheap"></a>offheap</h4>
-<div class="paragraph">
-<p>如果数据不可变，只作查询，也可以考虑 offheap，但局限性较大。</p>
-</div>
-</div>
-<div class="sect3">
-<h4 id="true减少变量逃逸"><a class="anchor" href="#true减少变量逃逸"></a>减少变量逃逸</h4>
-<div class="paragraph">
-<p>使用 go build -gcflags="-m -m" 来分析逃逸。</p>
-</div>
-<div class="paragraph">
-<p>如果要分析某个 package 内的逃逸情况，可以打全 package 名，例如 go build -gcflags="-m -m" github.com/cch123/elasticsql</p>
-</div>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true过多的调度-cpu-占用例如火焰图中schedule-有一大条"><a class="anchor" href="#true过多的调度-cpu-占用例如火焰图中schedule-有一大条"></a>过多的调度 CPU 占用(例如火焰图中，schedule 有一大条)</h3>
-<div class="paragraph">
-<p>类似 fasthttp 的 workerpool。</p>
-</div>
-<div class="paragraph">
-<p><a href="https://github.com/valyala/fasthttp/blob/master/workerpool.go#L19" class="bare">https://github.com/valyala/fasthttp/blob/master/workerpool.go#L19</a></p>
-</div>
-<div class="paragraph">
-<p>创建好的 goroutine 可以反复使用，并且自己实现可以控制最大的并发 worker 数。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true锁冲突"><a class="anchor" href="#true锁冲突"></a>锁冲突</h3>
-<div class="paragraph">
-<p>通过阶梯加压，观察 goroutine 的变化趋势。当触发锁瓶颈时，会出现大量等锁的 goroutine。</p>
-</div>
-<div class="sect3">
-<h4 id="true原因"><a class="anchor" href="#true原因"></a>原因</h4>
-<div class="paragraph">
-<p>临界区太大，其中包含系统调用。</p>
-</div>
-<div class="paragraph">
-<p>有些锁是避免不了的，例如 fs.Write，一定有锁，且该锁在 runtime 内部。</p>
-</div>
-<div class="paragraph">
-<p>性能敏感场合，全局锁，比如 rand 的全局锁。单机 10w+ QPS 即可能触发该瓶颈(和环境以及程序行为有关)</p>
-</div>
-<div class="paragraph">
-<p>有些开源库设计是一个 struct 对应一个 sync.Pool，这种时候，如果你不对该 struct 进行复用，就会触发 runtime 中的锁冲突：</p>
-</div>
-<div class="paragraph">
-<p>TODO</p>
-</div>
-</div>
-<div class="sect3">
-<h4 id="true解决方案"><a class="anchor" href="#true解决方案"></a>解决方案</h4>
-<div class="ulist">
-<ul>
-<li>
-<p>map → sync.Map。</p>
-</li>
-<li>
-<p>换用无锁结构。</p>
-</li>
-<li>
-<p>分段锁</p>
-</li>
-<li>
-<p>copy on write</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true程序局部性"><a class="anchor" href="#true程序局部性"></a>程序局部性</h3>
-<div class="sect3">
-<h4 id="truefalse-sharing"><a class="anchor" href="#truefalse-sharing"></a>false sharing</h4>
-<div class="paragraph">
-<p>时间局部性、空间局部性</p>
-</div>
-<div class="exampleblock">
-<div class="content">
-<div class="paragraph">
-<p>var semtable [semTabSize]struct {
- root semaRoot
- pad [cpu.CacheLinePadSize - unsafe.Sizeof(semaRoot{})]byte
-}</p>
-</div>
-</div>
-</div>
-<div class="exampleblock">
-<div class="content">
-<div class="paragraph">
-<p>var timers [timersLen]struct {
- timersBucket</p>
-</div>
-<div class="literalblock">
-<div class="content">
-<pre> // The padding should eliminate false sharing
- // between timersBucket values.
- pad [cpu.CacheLinePadSize - unsafe.Sizeof(timersBucket{})%cpu.CacheLinePadSize]byte
-}</pre>
-</div>
-</div>
-</div>
-</div>
-<div class="paragraph">
-<p>类似下面的二维数组，怎么遍历更快？</p>
-</div>
-<div class="exampleblock">
-<div class="content">
-<div class="paragraph">
-<p>var a = [10000][10000]int{}</p>
-</div>
-</div>
-</div>
-<div class="paragraph">
-<p>在标准库中，考虑到局部性而实现的 sort 的例子：</p>
-</div>
-<div class="exampleblock">
-<div class="content">
-<div class="paragraph">
-<p>func quickSort_func(data lessSwap, a, b, maxDepth int) {
- for b-a > 12 {
- if maxDepth == 0 {
- heapSort_func(data, a, b)
- return
- }
- maxDepth--
- mlo, mhi := doPivot_func(data, a, b)
- if mlo-a < b-mhi {
- quickSort_func(data, a, mlo, maxDepth)
- a = mhi
- } else {
- quickSort_func(data, mhi, b, maxDepth)
- b = mlo
- }
- }
- if b-a > 1 {
- for i := a + 6; i < b; i++ {
- if data.Less(i, i-6) {
- data.Swap(i, i-6)
- }
- }
- insertionSort_func(data, a, b)
- }
-}</p>
-</div>
-</div>
-</div>
-</div>
-<div class="sect3">
-<h4 id="truetrue-sharing"><a class="anchor" href="#truetrue-sharing"></a>true sharing</h4>
-<div class="paragraph">
-<p>这时候一般都有锁，所以本质上还是怎么降低锁的粒度。</p>
-</div>
-<div class="quoteblock">
-<blockquote>
-<div class="paragraph">
-<p>sync: RWMutex scales poorly with CPU count</p>
-</div>
-</blockquote>
-</div>
-</div>
-</div>
-<div class="sect2">
-<h3 id="truetimer-性能问题"><a class="anchor" href="#truetimer-性能问题"></a>timer 性能问题</h3>
-<div class="ulist">
-<ul>
-<li>
-<p>老版本的 timer 会有大量的 syscall → <a href="https://github.com/golang/go/issues/25471" class="bare">https://github.com/golang/go/issues/25471</a></p>
-</li>
-</ul>
-</div>
-<div class="exampleblock">
-<div class="content">
-<div class="paragraph">
-<p>go1.13</p>
-</div>
-<div class="paragraph">
-<p>% time seconds usecs/call calls errors syscall
------- ----------- ----------- --------- --------- ----------------
- 84.00 12.007993 459 26148 3874 futex
- 11.43 1.634512 146 11180 nanosleep
- 4.45 0.635987 32 20185 sched_yield</p>
-</div>
-<div class="paragraph">
-<p>go1.14</p>
-</div>
-<div class="paragraph">
-<p>% time seconds usecs/call calls errors syscall
------- ----------- ----------- --------- --------- ----------------
- 58.78 4.837332 174 27770 4662 futex
- 19.50 1.605189 440 3646 nanosleep
- 11.55 0.950730 44 21569 epoll_pwait
- 9.75 0.802715 36 22181 sched_yield:w</p>
-</div>
-</div>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>用时间轮实现粗粒度的时间库</p>
-</li>
-</ul>
-</div>
-<div class="paragraph">
-<p>可以搜搜大量的 timewheel 库。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true汇编优化"><a class="anchor" href="#true汇编优化"></a>汇编优化</h3>
-<div class="paragraph">
-<p>SIMD 优化，如 math 库。gonum 中也有一些例子。
-无法跨平台，如未来碰到国产化需求要上 ARM、龙芯(MIPS) 就尴尬了。</p>
-</div>
-<div class="paragraph">
-<p><a href="https://github.com/gonum/gonum/tree/master/internal/asm/f64" class="bare">https://github.com/gonum/gonum/tree/master/internal/asm/f64</a></p>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="true语言本身的一些缺陷"><a class="anchor" href="#true语言本身的一些缺陷"></a>语言本身的一些缺陷</h2>
-<div class="sectionbody">
-<div class="sect2">
-<h3 id="true越压越差"><a class="anchor" href="#true越压越差"></a>越压越差</h3>
-
-</div>
-<div class="sect2">
-<h3 id="true调度和锁"><a class="anchor" href="#true调度和锁"></a>调度和锁</h3>
-<div class="paragraph">
-<p>调度 + 锁出问题，难复现，难定位</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true不注意造成死循环会让整个进程-hang-住"><a class="anchor" href="#true不注意造成死循环会让整个进程-hang-住"></a>不注意造成死循环会让整个进程 hang 住</h3>
-<div class="paragraph">
-<p>GC 需要抢占所有 goroutine，老版本的抢占需要用户协程在 morestack 时主动退出。</p>
-</div>
-<div class="paragraph">
-<p>卡 gcwaiting。</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true物理机负载高时延迟非线性增长"><a class="anchor" href="#true物理机负载高时延迟非线性增长"></a>物理机负载高时，延迟非线性增长</h3>
-<div class="paragraph">
-<p>TODO</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true调度导致-cpu-密集型业务超时"><a class="anchor" href="#true调度导致-cpu-密集型业务超时"></a>调度导致 CPU 密集型业务超时</h3>
-<div class="paragraph">
-<p>TODO，bcrypt 的例子</p>
-</div>
-<div class="paragraph">
-<p>因为调度导致的全部超时</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true老版本的问题"><a class="anchor" href="#true老版本的问题"></a>老版本的问题</h3>
-<div class="sect3">
-<h4 id="truesync-pool-在-gc-时全清空"><a class="anchor" href="#truesync-pool-在-gc-时全清空"></a>sync.Pool 在 GC 时全清空</h4>
-<div class="paragraph">
-<p>导致在每一轮 GC 后都有延迟抖动，升级 1.13 后长尾请求有改善。</p>
-</div>
-</div>
-</div>
-<div class="sect2">
-<h3 id="true当前问题定位工具的局限性"><a class="anchor" href="#true当前问题定位工具的局限性"></a>当前问题定位工具的局限性</h3>
-<div class="paragraph">
-<p>难以定位抖动问题。</p>
-</div>
-<div class="paragraph">
-<p>无论 pprof、perf、fgprof、trace 都是人肉触发，抖动时人又不在系统旁边。</p>
-</div>
-<div class="paragraph">
-<p>这种情况需要 self-aware 的 profile dump 方式来解决问题。</p>
-</div>
-<div class="paragraph">
-<p>或者向 Google 看齐:</p>
-</div>
-<div class="sect3">
-<h4 id="truecontinuous-profiling"><a class="anchor" href="#truecontinuous-profiling"></a>continuous profiling</h4>
-<div class="paragraph">
-<p>早发现，早治疗。</p>
-</div>
-</div>
-</div>
-</div>
-</div>
-</div>
-<div id="footer">
-<div id="footer-text">
-Last updated 2020-09-10 01:34:10 +0800
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+/* Uncomment @import statement to use as custom stylesheet */
+/*@import "https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700";*/
+article,aside,details,figcaption,figure,footer,header,hgroup,main,nav,section{display:block}
+audio,video{display:inline-block}
+audio:not([controls]){display:none;height:0}
+html{font-family:sans-serif;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%}
+a{background:none}
+a:focus{outline:thin dotted}
+a:active,a:hover{outline:0}
+h1{font-size:2em;margin:.67em 0}
+abbr[title]{border-bottom:1px dotted}
+b,strong{font-weight:bold}
+dfn{font-style:italic}
+hr{-moz-box-sizing:content-box;box-sizing:content-box;height:0}
+mark{background:#ff0;color:#000}
+code,kbd,pre,samp{font-family:monospace;font-size:1em}
+pre{white-space:pre-wrap}
+q{quotes:"\201C" "\201D" "\2018" "\2019"}
+small{font-size:80%}
+sub,sup{font-size:75%;line-height:0;position:relative;vertical-align:baseline}
+sup{top:-.5em}
+sub{bottom:-.25em}
+img{border:0}
+svg:not(:root){overflow:hidden}
+figure{margin:0}
+fieldset{border:1px solid silver;margin:0 2px;padding:.35em .625em .75em}
+legend{border:0;padding:0}
+button,input,select,textarea{font-family:inherit;font-size:100%;margin:0}
+button,input{line-height:normal}
+button,select{text-transform:none}
+button,html input[type="button"],input[type="reset"],input[type="submit"]{-webkit-appearance:button;cursor:pointer}
+button[disabled],html input[disabled]{cursor:default}
+input[type="checkbox"],input[type="radio"]{box-sizing:border-box;padding:0}
+button::-moz-focus-inner,input::-moz-focus-inner{border:0;padding:0}
+textarea{overflow:auto;vertical-align:top}
+table{border-collapse:collapse;border-spacing:0}
+*,*::before,*::after{-moz-box-sizing:border-box;-webkit-box-sizing:border-box;box-sizing:border-box}
+html,body{font-size:100%}
+body{background:#fff;color:rgba(0,0,0,.8);padding:0;margin:0;font-family:"Noto Serif","DejaVu Serif",serif;font-weight:400;font-style:normal;line-height:1;position:relative;cursor:auto;tab-size:4;-moz-osx-font-smoothing:grayscale;-webkit-font-smoothing:antialiased}
+a:hover{cursor:pointer}
+img,object,embed{max-width:100%;height:auto}
+object,embed{height:100%}
+img{-ms-interpolation-mode:bicubic}
+.left{float:left!important}
+.right{float:right!important}
+.text-left{text-align:left!important}
+.text-right{text-align:right!important}
+.text-center{text-align:center!important}
+.text-justify{text-align:justify!important}
+.hide{display:none}
+img,object,svg{display:inline-block;vertical-align:middle}
+textarea{height:auto;min-height:50px}
+select{width:100%}
+.center{margin-left:auto;margin-right:auto}
+.stretch{width:100%}
+.subheader,.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{line-height:1.45;color:#7a2518;font-weight:400;margin-top:0;margin-bottom:.25em}
+div,dl,dt,dd,ul,ol,li,h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6,pre,form,p,blockquote,th,td{margin:0;padding:0;direction:ltr}
+a{color:#2156a5;text-decoration:underline;line-height:inherit}
+a:hover,a:focus{color:#1d4b8f}
+a img{border:0}
+p{font-family:inherit;font-weight:400;font-size:1em;line-height:1.6;margin-bottom:1.25em;text-rendering:optimizeLegibility}
+p aside{font-size:.875em;line-height:1.35;font-style:italic}
+h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{font-family:"Open Sans","DejaVu Sans",sans-serif;font-weight:300;font-style:normal;color:#ba3925;text-rendering:optimizeLegibility;margin-top:1em;margin-bottom:.5em;line-height:1.0125em}
+h1 small,h2 small,h3 small,#toctitle small,.sidebarblock>.content>.title small,h4 small,h5 small,h6 small{font-size:60%;color:#e99b8f;line-height:0}
+h1{font-size:2.125em}
+h2{font-size:1.6875em}
+h3,#toctitle,.sidebarblock>.content>.title{font-size:1.375em}
+h4,h5{font-size:1.125em}
+h6{font-size:1em}
+hr{border:solid #dddddf;border-width:1px 0 0;clear:both;margin:1.25em 0 1.1875em;height:0}
+em,i{font-style:italic;line-height:inherit}
+strong,b{font-weight:bold;line-height:inherit}
+small{font-size:60%;line-height:inherit}
+code{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;font-weight:400;color:rgba(0,0,0,.9)}
+ul,ol,dl{font-size:1em;line-height:1.6;margin-bottom:1.25em;list-style-position:outside;font-family:inherit}
+ul,ol{margin-left:1.5em}
+ul li ul,ul li ol{margin-left:1.25em;margin-bottom:0;font-size:1em}
+ul.square li ul,ul.circle li ul,ul.disc li ul{list-style:inherit}
+ul.square{list-style-type:square}
+ul.circle{list-style-type:circle}
+ul.disc{list-style-type:disc}
+ol li ul,ol li ol{margin-left:1.25em;margin-bottom:0}
+dl dt{margin-bottom:.3125em;font-weight:bold}
+dl dd{margin-bottom:1.25em}
+abbr,acronym{text-transform:uppercase;font-size:90%;color:rgba(0,0,0,.8);border-bottom:1px dotted #ddd;cursor:help}
+abbr{text-transform:none}
+blockquote{margin:0 0 1.25em;padding:.5625em 1.25em 0 1.1875em;border-left:1px solid #ddd}
+blockquote cite{display:block;font-size:.9375em;color:rgba(0,0,0,.6)}
+blockquote cite::before{content:"\2014 \0020"}
+blockquote cite a,blockquote cite a:visited{color:rgba(0,0,0,.6)}
+blockquote,blockquote p{line-height:1.6;color:rgba(0,0,0,.85)}
+@media screen and (min-width:768px){h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2}
+h1{font-size:2.75em}
+h2{font-size:2.3125em}
+h3,#toctitle,.sidebarblock>.content>.title{font-size:1.6875em}
+h4{font-size:1.4375em}}
+table{background:#fff;margin-bottom:1.25em;border:solid 1px #dedede}
+table thead,table tfoot{background:#f7f8f7}
+table thead tr th,table thead tr td,table tfoot tr th,table tfoot tr td{padding:.5em .625em .625em;font-size:inherit;color:rgba(0,0,0,.8);text-align:left}
+table tr th,table tr td{padding:.5625em .625em;font-size:inherit;color:rgba(0,0,0,.8)}
+table tr.even,table tr.alt{background:#f8f8f7}
+table thead tr th,table tfoot tr th,table tbody tr td,table tr td,table tfoot tr td{display:table-cell;line-height:1.6}
+h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2;word-spacing:-.05em}
+h1 strong,h2 strong,h3 strong,#toctitle strong,.sidebarblock>.content>.title strong,h4 strong,h5 strong,h6 strong{font-weight:400}
+.clearfix::before,.clearfix::after,.float-group::before,.float-group::after{content:" ";display:table}
+.clearfix::after,.float-group::after{clear:both}
+:not(pre):not([class^=L])>code{font-size:.9375em;font-style:normal!important;letter-spacing:0;padding:.1em .5ex;word-spacing:-.15em;background:#f7f7f8;-webkit-border-radius:4px;border-radius:4px;line-height:1.45;text-rendering:optimizeSpeed;word-wrap:break-word}
+:not(pre)>code.nobreak{word-wrap:normal}
+:not(pre)>code.nowrap{white-space:nowrap}
+pre{color:rgba(0,0,0,.9);font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;line-height:1.45;text-rendering:optimizeSpeed}
+pre code,pre pre{color:inherit;font-size:inherit;line-height:inherit}
+pre>code{display:block}
+pre.nowrap,pre.nowrap pre{white-space:pre;word-wrap:normal}
+em em{font-style:normal}
+strong strong{font-weight:400}
+.keyseq{color:rgba(51,51,51,.8)}
+kbd{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;display:inline-block;color:rgba(0,0,0,.8);font-size:.65em;line-height:1.45;background:#f7f7f7;border:1px solid #ccc;-webkit-border-radius:3px;border-radius:3px;-webkit-box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em white inset;box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em #fff inset;margin:0 .15em;padding:.2em .5em;vertical-align:middle;position:relative;top:-.1em;white-space:nowrap}
+.keyseq kbd:first-child{margin-left:0}
+.keyseq kbd:last-child{margin-right:0}
+.menuseq,.menuref{color:#000}
+.menuseq b:not(.caret),.menuref{font-weight:inherit}
+.menuseq{word-spacing:-.02em}
+.menuseq b.caret{font-size:1.25em;line-height:.8}
+.menuseq i.caret{font-weight:bold;text-align:center;width:.45em}
+b.button::before,b.button::after{position:relative;top:-1px;font-weight:400}
+b.button::before{content:"[";padding:0 3px 0 2px}
+b.button::after{content:"]";padding:0 2px 0 3px}
+p a>code:hover{color:rgba(0,0,0,.9)}
+#header,#content,#footnotes,#footer{width:100%;margin-left:auto;margin-right:auto;margin-top:0;margin-bottom:0;max-width:62.5em;*zoom:1;position:relative;padding-left:.9375em;padding-right:.9375em}
+#header::before,#header::after,#content::before,#content::after,#footnotes::before,#footnotes::after,#footer::before,#footer::after{content:" ";display:table}
+#header::after,#content::after,#footnotes::after,#footer::after{clear:both}
+#content{margin-top:1.25em}
+#content::before{content:none}
+#header>h1:first-child{color:rgba(0,0,0,.85);margin-top:2.25rem;margin-bottom:0}
+#header>h1:first-child+#toc{margin-top:8px;border-top:1px solid #dddddf}
+#header>h1:only-child,body.toc2 #header>h1:nth-last-child(2){border-bottom:1px solid #dddddf;padding-bottom:8px}
+#header .details{border-bottom:1px solid #dddddf;line-height:1.45;padding-top:.25em;padding-bottom:.25em;padding-left:.25em;color:rgba(0,0,0,.6);display:-ms-flexbox;display:-webkit-flex;display:flex;-ms-flex-flow:row wrap;-webkit-flex-flow:row wrap;flex-flow:row wrap}
+#header .details span:first-child{margin-left:-.125em}
+#header .details span.email a{color:rgba(0,0,0,.85)}
+#header .details br{display:none}
+#header .details br+span::before{content:"\00a0\2013\00a0"}
+#header .details br+span.author::before{content:"\00a0\22c5\00a0";color:rgba(0,0,0,.85)}
+#header .details br+span#revremark::before{content:"\00a0|\00a0"}
+#header #revnumber{text-transform:capitalize}
+#header #revnumber::after{content:"\00a0"}
+#content>h1:first-child:not([class]){color:rgba(0,0,0,.85);border-bottom:1px solid #dddddf;padding-bottom:8px;margin-top:0;padding-top:1rem;margin-bottom:1.25rem}
+#toc{border-bottom:1px solid #e7e7e9;padding-bottom:.5em}
+#toc>ul{margin-left:.125em}
+#toc ul.sectlevel0>li>a{font-style:italic}
+#toc ul.sectlevel0 ul.sectlevel1{margin:.5em 0}
+#toc ul{font-family:"Open Sans","DejaVu Sans",sans-serif;list-style-type:none}
+#toc li{line-height:1.3334;margin-top:.3334em}
+#toc a{text-decoration:none}
+#toc a:active{text-decoration:underline}
+#toctitle{color:#7a2518;font-size:1.2em}
+@media screen and (min-width:768px){#toctitle{font-size:1.375em}
+body.toc2{padding-left:15em;padding-right:0}
+#toc.toc2{margin-top:0!important;background:#f8f8f7;position:fixed;width:15em;left:0;top:0;border-right:1px solid #e7e7e9;border-top-width:0!important;border-bottom-width:0!important;z-index:1000;padding:1.25em 1em;height:100%;overflow:auto}
+#toc.toc2 #toctitle{margin-top:0;margin-bottom:.8rem;font-size:1.2em}
+#toc.toc2>ul{font-size:.9em;margin-bottom:0}
+#toc.toc2 ul ul{margin-left:0;padding-left:1em}
+#toc.toc2 ul.sectlevel0 ul.sectlevel1{padding-left:0;margin-top:.5em;margin-bottom:.5em}
+body.toc2.toc-right{padding-left:0;padding-right:15em}
+body.toc2.toc-right #toc.toc2{border-right-width:0;border-left:1px solid #e7e7e9;left:auto;right:0}}
+@media screen and (min-width:1280px){body.toc2{padding-left:20em;padding-right:0}
+#toc.toc2{width:20em}
+#toc.toc2 #toctitle{font-size:1.375em}
+#toc.toc2>ul{font-size:.95em}
+#toc.toc2 ul ul{padding-left:1.25em}
+body.toc2.toc-right{padding-left:0;padding-right:20em}}
+#content #toc{border-style:solid;border-width:1px;border-color:#e0e0dc;margin-bottom:1.25em;padding:1.25em;background:#f8f8f7;-webkit-border-radius:4px;border-radius:4px}
+#content #toc>:first-child{margin-top:0}
+#content #toc>:last-child{margin-bottom:0}
+#footer{max-width:100%;background:rgba(0,0,0,.8);padding:1.25em}
+#footer-text{color:rgba(255,255,255,.8);line-height:1.44}
+#content{margin-bottom:.625em}
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