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<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">eBPF 实践教程：基于 libbpf 和 CO-RE</li><li class="chapter-item expanded "><a href="../0-introduce/index.html"><strong aria-hidden="true">1.</strong> eBPF 入门开发实践教程一：介绍 eBPF 的基本概念、常见的开发工具</a></li><li class="chapter-item expanded "><a href="../1-helloworld/index.html"><strong aria-hidden="true">2.</strong> eBPF 入门开发实践教程二：Hello World，基本框架和开发流程</a></li><li class="chapter-item expanded "><a href="../2-kprobe-unlink/index.html"><strong aria-hidden="true">3.</strong> eBPF 入门开发实践教程二：在 eBPF 中使用 kprobe 监测捕获 unlink 系统调用</a></li><li class="chapter-item expanded "><a href="../3-fentry-unlink/index.html"><strong aria-hidden="true">4.</strong> eBPF 入门开发实践教程三：在 eBPF 中使用 fentry 监测捕获 unlink 系统调用</a></li><li class="chapter-item expanded "><a href="../4-opensnoop/index.html"><strong aria-hidden="true">5.</strong> eBPF 入门开发实践教程四：在 eBPF 中捕获进程打开文件的系统调用集合，使用全局变量过滤进程 pid</a></li><li class="chapter-item expanded "><a href="../5-uprobe-bashreadline/index.html"><strong aria-hidden="true">6.</strong> eBPF 入门开发实践教程五：在 eBPF 中使用 uprobe 捕获 bash 的 readline 函数调用</a></li><li class="chapter-item expanded "><a href="../6-sigsnoop/index.html"><strong aria-hidden="true">7.</strong> eBPF 入门开发实践教程六：捕获进程发送信号的系统调用集合，使用 hash map 保存状态</a></li><li class="chapter-item expanded "><a href="../7-execsnoop/index.html"><strong aria-hidden="true">8.</strong> eBPF 入门实践教程七：捕获进程执行/退出时间，通过 perf event array 向用户态打印输出</a></li><li class="chapter-item expanded "><a href="../8-exitsnoop/index.html"><strong aria-hidden="true">9.</strong> eBPF 入门开发实践教程八：在 eBPF 中使用 exitsnoop 监控进程退出事件，使用 ring buffer 向用户态打印输出</a></li><li class="chapter-item expanded "><a href="../9-runqlat/index.html"><strong aria-hidden="true">10.</strong> eBPF 入门开发实践教程九：一个 Linux 内核 BPF 程序，通过柱状图来总结调度程序运行队列延迟，显示任务等待运行在 CPU 上的时间长度</a></li><li class="chapter-item expanded "><a href="../10-hardirqs/index.html"><strong aria-hidden="true">11.</strong> eBPF 入门开发实践教程十：在 eBPF 中使用 hardirqs 或 softirqs 捕获中断事件</a></li><li class="chapter-item expanded "><a href="../11-bootstrap/index.html"><strong aria-hidden="true">12.</strong> eBPF 入门开发实践教程十一：在 eBPF 中使用 bootstrap 开发用户态程序并跟踪 exec() 和 exit() 系统调用</a></li><li class="chapter-item expanded "><a href="../13-tcpconnlat/index.html"><strong aria-hidden="true">13.</strong> eBPF入门实践教程：使用 libbpf-bootstrap 开发程序统计 TCP 连接延时</a></li><li class="chapter-item expanded "><a href="../13-tcpconnlat/tcpconnlat.html"><strong aria-hidden="true">14.</strong> eBPF 入门实践教程：编写 eBPF 程序 tcpconnlat 测量 tcp 连接延时</a></li><li class="chapter-item expanded "><a href="../14-tcpstates/index.html"><strong aria-hidden="true">15.</strong> eBPF入门实践教程：使用 libbpf-bootstrap 开发程序统计 TCP 连接延时</a></li><li class="chapter-item expanded "><a href="../15-tcprtt/index.html" class="active"><strong aria-hidden="true">16.</strong> eBPF 入门实践教程：编写 eBPF 程序 Tcprtt 测量 TCP 连接的往返时间</a></li><li class="chapter-item expanded "><a href="../16-memleak/index.html"><strong aria-hidden="true">17.</strong> eBPF 入门实践教程：编写 eBPF 程序 Memleak 监控内存泄漏</a></li><li class="chapter-item expanded "><a href="../17-biopattern/index.html"><strong aria-hidden="true">18.</strong> eBPF 入门实践教程：编写 eBPF 程序 Biopattern: 统计随机/顺序磁盘 I/O</a></li><li class="chapter-item expanded "><a href="../18-further-reading/index.html"><strong aria-hidden="true">19.</strong> 更多的参考资料</a></li><li class="chapter-item expanded "><a href="../19-lsm-connect/index.html"><strong aria-hidden="true">20.</strong> eBPF 入门实践教程：使用 LSM 进行安全检测防御</a></li><li class="chapter-item expanded "><a href="../20-tc/index.html"><strong aria-hidden="true">21.</strong> eBPF 入门实践教程：使用 eBPF 进行 tc 流量控制</a></li><li class="chapter-item expanded affix "><li class="part-title">bcc 开发者教程</li><li class="chapter-item expanded "><a href="../bcc-documents/kernel-versions.html"><strong aria-hidden="true">22.</strong> BPF Features by Linux Kernel Version</a></li><li class="chapter-item expanded "><a href="../bcc-documents/kernel_config.html"><strong aria-hidden="true">23.</strong> Kernel Configuration for BPF Features</a></li><li class="chapter-item expanded "><a href="../bcc-documents/reference_guide.html"><strong aria-hidden="true">24.</strong> bcc Reference Guide</a></li><li class="chapter-item expanded "><a href="../bcc-documents/special_filtering.html"><strong aria-hidden="true">25.</strong> Special Filtering</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial.html"><strong aria-hidden="true">26.</strong> bcc Tutorial</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial_bcc_python_developer.html"><strong aria-hidden="true">27.</strong> bcc Python Developer Tutorial</a></li></ol>
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<h1 id="ebpf-入门实践教程编写-ebpf-程序-tcprtt-测量-tcp-连接的往返时间"><a class="header" href="#ebpf-入门实践教程编写-ebpf-程序-tcprtt-测量-tcp-连接的往返时间">eBPF 入门实践教程：编写 eBPF 程序 Tcprtt 测量 TCP 连接的往返时间</a></h1>
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<h2 id="背景"><a class="header" href="#背景">背景</a></h2>
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<p>网络质量在互联网社会中是一个很重要的因素。导致网络质量差的因素有很多，可能是硬件因素导致，也可能是程序
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写的不好导致。为了能更好地定位网络问题，<code>tcprtt</code> 工具被提出。它可以监测TCP链接的往返时间，从而分析
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网络质量，帮助用户定位问题来源。</p>
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<p>当有tcp链接建立时，该工具会自动根据当前系统的支持情况，选择合适的执行函数。
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在执行函数中，<code>tcprtt</code>会收集tcp链接的各项基本信息，包括地址，源端口，目标端口，耗时
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等等，并将其更新到直方图的map中。运行结束后通过用户态代码，展现给用户。</p>
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<h2 id="编写-ebpf-程序"><a class="header" href="#编写-ebpf-程序">编写 eBPF 程序</a></h2>
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<pre><code class="language-c">// SPDX-License-Identifier: GPL-2.0
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// Copyright (c) 2021 Wenbo Zhang
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#include <vmlinux.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_core_read.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_endian.h>
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#include "tcprtt.h"
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#include "bits.bpf.h"
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#include "maps.bpf.h"
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char LICENSE[] SEC("license") = "Dual BSD/GPL";
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const volatile bool targ_laddr_hist = false;
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const volatile bool targ_raddr_hist = false;
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const volatile bool targ_show_ext = false;
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const volatile __u16 targ_sport = 0;
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const volatile __u16 targ_dport = 0;
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const volatile __u32 targ_saddr = 0;
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const volatile __u32 targ_daddr = 0;
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const volatile bool targ_ms = false;
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#define MAX_ENTRIES 10240
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/// @sample {"interval": 1000, "type" : "log2_hist"}
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__uint(max_entries, MAX_ENTRIES);
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__type(key, u64);
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__type(value, struct hist);
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} hists SEC(".maps");
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static struct hist zero;
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SEC("fentry/tcp_rcv_established")
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int BPF_PROG(tcp_rcv, struct sock *sk)
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{
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const struct inet_sock *inet = (struct inet_sock *)(sk);
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struct tcp_sock *ts;
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struct hist *histp;
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u64 key, slot;
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u32 srtt;
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if (targ_sport && targ_sport != inet->inet_sport)
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return 0;
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if (targ_dport && targ_dport != sk->__sk_common.skc_dport)
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return 0;
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if (targ_saddr && targ_saddr != inet->inet_saddr)
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return 0;
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if (targ_daddr && targ_daddr != sk->__sk_common.skc_daddr)
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return 0;
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if (targ_laddr_hist)
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key = inet->inet_saddr;
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else if (targ_raddr_hist)
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key = inet->sk.__sk_common.skc_daddr;
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else
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key = 0;
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histp = bpf_map_lookup_or_try_init(&hists, &key, &zero);
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if (!histp)
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return 0;
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ts = (struct tcp_sock *)(sk);
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srtt = BPF_CORE_READ(ts, srtt_us) >> 3;
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if (targ_ms)
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srtt /= 1000U;
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slot = log2l(srtt);
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if (slot >= MAX_SLOTS)
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slot = MAX_SLOTS - 1;
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__sync_fetch_and_add(&histp->slots[slot], 1);
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if (targ_show_ext) {
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__sync_fetch_and_add(&histp->latency, srtt);
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__sync_fetch_and_add(&histp->cnt, 1);
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}
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return 0;
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}
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</code></pre>
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<p>这段代码是基于eBPF的网络延迟分析工具，它通过hooking TCP协议栈中的tcp_rcv_established函数来统计TCP连接的RTT分布。下面是这段代码的主要工作原理：</p>
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<ol>
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<li>
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<p>首先定义了一个名为"hists"的eBPF哈希表，用于保存RTT直方图数据。</p>
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</li>
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<li>
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<p>当tcp_rcv_established函数被调用时，它首先从传入的socket结构体中获取TCP相关信息，包括本地/远程IP地址、本地/远程端口号以及TCP状态信息等。</p>
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</li>
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<li>
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<p>接下来，代码会检查用户指定的条件是否匹配当前TCP连接。如果匹配失败，则直接返回。</p>
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</li>
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<li>
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<p>如果匹配成功，则从"hists"哈希表中查找与本地/远程IP地址匹配的直方图数据。如果该IP地址的直方图不存在，则创建一个新的直方图并插入哈希表中。</p>
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</li>
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<li>
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<p>接下来，代码会从socket结构体中获取当前TCP连接的RTT(srtt)，并根据用户设置的选项来将srtt值进行处理。如果用户设置了"-ms"选项，则将srtt值除以1000。</p>
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</li>
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<li>
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<p>接着，代码会将srtt值转换为直方图的槽位(slot)，并将该槽位的计数器+1。</p>
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</li>
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<li>
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<p>如果用户设置了"-show-ext"选项，则还会累加直方图的总延迟(latency)和计数(cnt)。</p>
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</li>
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</ol>
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<h2 id="编译运行"><a class="header" href="#编译运行">编译运行</a></h2>
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<p>eunomia-bpf 是一个结合 Wasm 的开源 eBPF 动态加载运行时和开发工具链，它的目的是简化 eBPF 程序的开发、构建、分发、运行。可以参考 <a href="https://github.com/eunomia-bpf/eunomia-bpf">https://github.com/eunomia-bpf/eunomia-bpf</a> 下载和安装 ecc 编译工具链和 ecli 运行时。我们使用 eunomia-bpf 编译运行这个例子。</p>
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<p>Compile:</p>
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<pre><code class="language-shell">docker run -it -v `pwd`/:/src/ yunwei37/ebpm:latest
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</code></pre>
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<p>或者</p>
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<pre><code class="language-console">$ ecc runqlat.bpf.c runqlat.h
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Compiling bpf object...
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Generating export types...
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Packing ebpf object and config into package.json...
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</code></pre>
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<p>Run:</p>
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<pre><code class="language-console">$ sudo ecli run package.json -h
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A simple eBPF program
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Usage: package.json [OPTIONS]
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Options:
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--verbose Whether to show libbpf debug information
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--targ_laddr_hist Set value of `bool` variable targ_laddr_hist
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--targ_raddr_hist Set value of `bool` variable targ_raddr_hist
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--targ_show_ext Set value of `bool` variable targ_show_ext
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--targ_sport <targ_sport> Set value of `__u16` variable targ_sport
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--targ_dport <targ_dport> Set value of `__u16` variable targ_dport
|
||
--targ_saddr <targ_saddr> Set value of `__u32` variable targ_saddr
|
||
--targ_daddr <targ_daddr> Set value of `__u32` variable targ_daddr
|
||
--targ_ms Set value of `bool` variable targ_ms
|
||
-h, --help Print help
|
||
-V, --version Print version
|
||
|
||
Built with eunomia-bpf framework.
|
||
See https://github.com/eunomia-bpf/eunomia-bpf for more information.
|
||
|
||
$ sudo ecli run package.json
|
||
key = 0
|
||
latency = 0
|
||
cnt = 0
|
||
|
||
(unit) : count distribution
|
||
0 -> 1 : 0 | |
|
||
2 -> 3 : 0 | |
|
||
4 -> 7 : 0 | |
|
||
8 -> 15 : 0 | |
|
||
16 -> 31 : 0 | |
|
||
32 -> 63 : 0 | |
|
||
64 -> 127 : 0 | |
|
||
128 -> 255 : 0 | |
|
||
256 -> 511 : 0 | |
|
||
512 -> 1023 : 4 |******************** |
|
||
1024 -> 2047 : 1 |***** |
|
||
2048 -> 4095 : 0 | |
|
||
4096 -> 8191 : 8 |****************************************|
|
||
|
||
key = 0
|
||
latency = 0
|
||
cnt = 0
|
||
|
||
(unit) : count distribution
|
||
0 -> 1 : 0 | |
|
||
2 -> 3 : 0 | |
|
||
4 -> 7 : 0 | |
|
||
8 -> 15 : 0 | |
|
||
16 -> 31 : 0 | |
|
||
32 -> 63 : 0 | |
|
||
64 -> 127 : 0 | |
|
||
128 -> 255 : 0 | |
|
||
256 -> 511 : 0 | |
|
||
512 -> 1023 : 11 |*************************** |
|
||
1024 -> 2047 : 1 |** |
|
||
2048 -> 4095 : 0 | |
|
||
4096 -> 8191 : 16 |****************************************|
|
||
8192 -> 16383 : 4 |********** |
|
||
</code></pre>
|
||
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
|
||
<p>tcprtt是一个基于eBPF的TCP延迟分析工具。通过hooking TCP协议栈中的tcp_rcv_established函数来统计TCP连接的RTT分布，可以对指定的TCP连接进行RTT分布统计，并将结果保存到eBPF哈希表中。同时，这个工具支持多种条件过滤和RTT分布数据扩展功能，以便用户可以更好地进行网络性能分析和调优。</p>
|
||
<p>更多的例子和详细的开发指南，请参考 eunomia-bpf 的官方文档：<a href="https://github.com/eunomia-bpf/eunomia-bpf">https://github.com/eunomia-bpf/eunomia-bpf</a></p>
|
||
<p>完整的教程和源代码已经全部开源，可以在 <a href="https://github.com/eunomia-bpf/bpf-developer-tutorial">https://github.com/eunomia-bpf/bpf-developer-tutorial</a> 中查看。</p>
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