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<li class="toctree-l2"><a class="reference internal" href="../chapter4/3sv39-implementation-1.html">实现 SV39 多级页表机制（上）</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter4/7exercise.html">chapter4练习</a></li>
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<li class="toctree-l1 current has-children"><a class="reference internal" href="index.html">第五章：进程及进程管理</a><input checked="" class="toctree-checkbox" id="toctree-checkbox-13" name="toctree-checkbox-13" role="switch" type="checkbox"/><label for="toctree-checkbox-13"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="current">
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<li class="toctree-l2"><a class="reference internal" href="1process.html">与进程有关的重要系统调用</a></li>
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<li class="toctree-l2"><a class="reference internal" href="2core-data-structures.html">进程管理的核心数据结构</a></li>
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<li class="toctree-l2"><a class="reference internal" href="3implement-process-mechanism.html">进程管理机制的设计实现</a></li>
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<li class="toctree-l2 current current-page"><a class="current reference internal" href="#">chapter5练习</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter6/1file-descriptor.html">文件与文件描述符</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter6/1fs-interface.html">文件系统接口</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter6/2fs-implementation-1.html">简易文件系统 easy-fs (上)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter6/4exercise.html">chapter6练习</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter8/5exercise.html">chapter8 练习</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
<p class="caption" role="heading"><span class="caption-text">附录</span></p>
|
||
<ul>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-a/index.html">附录 A：Rust 系统编程资料</a><input class="toctree-checkbox" id="toctree-checkbox-17" name="toctree-checkbox-17" role="switch" type="checkbox"/><label for="toctree-checkbox-17"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-b/index.html">附录 B：常见工具的使用方法</a><input class="toctree-checkbox" id="toctree-checkbox-18" name="toctree-checkbox-18" role="switch" type="checkbox"/><label for="toctree-checkbox-18"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-c/index.html">附录 C：深入机器模式：RustSBI</a><input class="toctree-checkbox" id="toctree-checkbox-19" name="toctree-checkbox-19" role="switch" type="checkbox"/><label for="toctree-checkbox-19"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1"><a class="reference internal" href="../appendix-d/index.html">附录 D：RISC-V相关信息</a></li>
|
||
</ul>
|
||
<p class="caption" role="heading"><span class="caption-text">开发注记</span></p>
|
||
<ul>
|
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<li class="toctree-l1 has-children"><a class="reference internal" href="../setup-sphinx.html">修改和构建本项目</a><input class="toctree-checkbox" id="toctree-checkbox-20" name="toctree-checkbox-20" role="switch" type="checkbox"/><label for="toctree-checkbox-20"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
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<li class="toctree-l1 has-children"><a class="reference internal" href="../rest-example.html">reStructuredText 基本语法</a><input class="toctree-checkbox" id="toctree-checkbox-21" name="toctree-checkbox-21" role="switch" type="checkbox"/><label for="toctree-checkbox-21"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
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<div class="main">
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<article role="main">
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<div class="content-icon-container">
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<div class="theme-toggle-container theme-toggle-content">
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<button class="theme-toggle">
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<div class="visually-hidden">Toggle Light / Dark / Auto color theme</div>
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<svg class="theme-icon-when-auto"><use href="#svg-sun-half"></use></svg>
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<div class="visually-hidden">Toggle table of contents sidebar</div>
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<i class="icon"><svg><use href="#svg-toc"></use></svg></i>
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</label>
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</div>
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||
<div class="section" id="chapter5">
|
||
<h1>chapter5练习<a class="headerlink" href="#chapter5" title="永久链接至标题">¶</a></h1>
|
||
<div class="section" id="lab3">
|
||
<h2>Lab3 编程作业<a class="headerlink" href="#lab3" title="永久链接至标题">¶</a></h2>
|
||
<div class="section" id="id1">
|
||
<h3>进程创建<a class="headerlink" href="#id1" title="永久链接至标题">¶</a></h3>
|
||
<p>大家一定好奇过为啥进程创建要用 fork + exec 这么一个奇怪的系统调用，就不能直接搞一个新进程吗？
|
||
思而不学则殆，我们就来试一试！这章的编程练习请大家实现一个完全 DIY 的系统调用 spawn，用以创建一个新进程。</p>
|
||
<p>spawn 系统调用定义( <a class="reference external" href="https://man7.org/linux/man-pages/man3/posix_spawn.3.html">标准spawn看这里</a> )：</p>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="k">fn</span> <span class="nf">sys_spawn</span><span class="p">(</span><span class="n">path</span>: <span class="o">*</span><span class="k">const</span><span class="w"> </span><span class="kt">u8</span><span class="p">)</span><span class="w"> </span>-> <span class="kt">isize</span>
|
||
</pre></div>
|
||
</div>
|
||
<ul class="simple">
|
||
<li><p>syscall ID: 400</p></li>
|
||
<li><p>功能：新建子进程，使其执行目标程序。</p></li>
|
||
<li><p>说明：成功返回子进程id，否则返回 -1。</p></li>
|
||
<li><dl class="simple">
|
||
<dt>可能的错误：</dt><dd><ul>
|
||
<li><p>无效的文件名。</p></li>
|
||
<li><p>进程池满/内存不足等资源错误。</p></li>
|
||
</ul>
|
||
</dd>
|
||
</dl>
|
||
</li>
|
||
</ul>
|
||
<p>TIPS：虽然测例很简单，但提醒读者 spawn <strong>不必</strong> 像 fork 一样复制父进程的地址空间。</p>
|
||
</div>
|
||
<div class="section" id="stride">
|
||
<h3>stride 调度算法<a class="headerlink" href="#stride" title="永久链接至标题">¶</a></h3>
|
||
<p>ch3 中我们实现的调度算法十分简单。现在我们要为我们的 os 实现一种带优先级的调度算法：stride 调度算法。</p>
|
||
<p>算法描述如下:</p>
|
||
<p>(1) 为每个进程设置一个当前 pass，表示该进程当前已经运行的“长度”。另外设置其对应的 stride
|
||
值（只与进程的优先权有关系），表示对应进程在调度后，pass 需要进行的累加值。</p>
|
||
<ol class="arabic simple" start="2">
|
||
<li><p>每次需要调度时，从当前 runnable 态的进程中选择 pass 最小的进程调度。对于获得调度的进程 P，将对应的 pass 加上其对应的步长 stride。</p></li>
|
||
<li><p>一个时间片后，回到上一步骤，重新调度当前 pass 最小的进程。</p></li>
|
||
</ol>
|
||
<p>可以证明，如果令 P.stride = BigStride / P.priority 其中 P.priority 表示进程的优先权（大于 1），而
|
||
BigStride 表示一个预先定义的大常数，则该调度方案为每个进程分配的时间将与其优先级成正比。证明过程我们在这里略去，有兴趣的同学可以在网上查找相关资料。</p>
|
||
<p>其他实验细节：</p>
|
||
<ul class="simple">
|
||
<li><p>stride 调度要求进程优先级 <span class="math notranslate nohighlight">\(\geq 2\)</span>，所以设定进程优先级 <span class="math notranslate nohighlight">\(\leq 1\)</span> 会导致错误。</p></li>
|
||
<li><p>进程初始 pass 设置为 0 即可。</p></li>
|
||
<li><p>进程初始优先级设置为 16。</p></li>
|
||
</ul>
|
||
<p>为了实现该调度算法，内核还要增加 set_prio 系统调用</p>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="c1">// syscall ID：140</span>
|
||
<span class="c1">// 设置当前进程优先级为 prio</span>
|
||
<span class="c1">// 参数：prio 进程优先级，要求 prio >= 2</span>
|
||
<span class="c1">// 返回值：如果输入合法则返回 prio，否则返回 -1</span>
|
||
<span class="k">fn</span> <span class="nf">sys_set_priority</span><span class="p">(</span><span class="n">prio</span>: <span class="kt">isize</span><span class="p">)</span><span class="w"> </span>-> <span class="kt">isize</span><span class="p">;</span><span class="w"></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>实现 tips:</p>
|
||
<ul class="simple">
|
||
<li><p>你可以在TCB加入新的字段来支持优先级等。</p></li>
|
||
<li><p>为了减少整数除的误差，BIG_STRIDE 一般需要很大，但为了不至于发生反转现象（详见问答作业），或许选择一个适中的数即可，当然能进行溢出处理就更好了。</p></li>
|
||
<li><p>stride 算法要找到 pass 最小的进程，使用优先级队列是效率不错的办法，但是我们的实验测例很简单，所以效率完全不是问题。事实上，很推荐使用暴力扫一遍的办法找最小值。</p></li>
|
||
<li><p>注意设置进程的初始优先级。</p></li>
|
||
</ul>
|
||
<div class="admonition attention">
|
||
<p class="admonition-title">注意</p>
|
||
<p>为了让大家能在本编程作业中使用 <code class="docutils literal notranslate"><span class="pre">Vec</span></code> 等数据结构，我们利用第三方库 <code class="docutils literal notranslate"><span class="pre">buddy_system_allocator</span></code>
|
||
为大家实现了堆内存分配器，相关代码位于 <code class="docutils literal notranslate"><span class="pre">mm/heap_allocator</span></code> 模块。</p>
|
||
<p>背景知识： <a class="reference external" href="https://rcore-os.github.io/rCore-Tutorial-Book-v3/chapter4/1rust-dynamic-allocation.html">Rust 中的动态内存分配</a></p>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id2">
|
||
<h3>实验要求<a class="headerlink" href="#id2" title="永久链接至标题">¶</a></h3>
|
||
<ul>
|
||
<li><p><a class="reference external" href="https://github.com/LearningOS/rust-based-os-comp2022/tree/main/os5-ref">lab3(os5)参考框架:</a></p></li>
|
||
<li><p>实验目录在 <code class="docutils literal notranslate"><span class="pre">os5</span></code> 。注意在reports中放入lab1-3的所有报告。</p></li>
|
||
<li><p>通过所有测例。</p>
|
||
<p>在 os5 目录下 <code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">run</span> <span class="pre">BASE=2</span></code> 加载所有测例， <code class="docutils literal notranslate"><span class="pre">ch5_usertest</span></code> 打包了所有你需要通过的测例，
|
||
你也可以通过修改这个文件调整本地测试的内容, 或者单独运行某测例来纠正特定的错误。 <code class="docutils literal notranslate"><span class="pre">ch5_stride</span></code>
|
||
检查 stride 调度算法是否满足公平性要求，六个子程序运行的次数应该大致与其优先级呈正比，测试通过标准是
|
||
<span class="math notranslate nohighlight">\(\max{\frac{runtimes}{prio}}/ \min{\frac{runtimes}{prio}} < 1.5\)</span>.</p>
|
||
<p>CI 的原理是用 <code class="docutils literal notranslate"><span class="pre">ch5_usertest</span></code> 替代 <code class="docutils literal notranslate"><span class="pre">ch5b_initproc</span></code> ，使内核在所有测例执行完后直接退出。</p>
|
||
<p>从本章开始，你的内核必须前向兼容，能通过前一章的所有测例。</p>
|
||
</li>
|
||
<li><p>开发并通过所有测例</p></li>
|
||
</ul>
|
||
<p>在 <code class="docutils literal notranslate"><span class="pre">YOUR_LAB3_REPO_DIR</span></code> 下进行编码（可学习参考 <code class="docutils literal notranslate"><span class="pre">os5-ref/src</span></code> 目录下的源代码，并在 <code class="docutils literal notranslate"><span class="pre">os5/src</span></code> 中完成编码），并进行编译测试。</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p><strong>测试方式</strong></p>
|
||
<p>你的实现只需且必须通过测例，建议读者感到困惑时先检查测例</p>
|
||
<p>如果实现正确，可在项目仓库的根目录下执行 <code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">test5</span></code> ，应该看到类似如下的显示输出：</p>
|
||
<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="gp"> $ </span><span class="nb">cd</span> YOUR_LAB3_REPO_DIR
|
||
<span class="gp"> $ </span>make test5
|
||
<span class="go"> ......</span>
|
||
<span class="go"> [rustsbi] RustSBI version 0.2.2, adapting to RISC-V SBI v1.0.0</span>
|
||
<span class="go"> .______ __ __ _______.___________. _______..______ __</span>
|
||
<span class="go"> | _ \ | | | | / | | / || _ \ | |</span>
|
||
<span class="go"> | |_) | | | | | | (----`---| |----`| (----`| |_) || |</span>
|
||
<span class="go"> | / | | | | \ \ | | \ \ | _ < | |</span>
|
||
<span class="go"> | |\ \----.| `--' |.----) | | | .----) | | |_) || |</span>
|
||
<span class="go"> | _| `._____| \______/ |_______/ |__| |_______/ |______/ |__|</span>
|
||
<span class="go"> [rustsbi] Implementation : RustSBI-QEMU Version 0.1.1</span>
|
||
<span class="go"> [rustsbi] Platform Name : riscv-virtio,qemu</span>
|
||
<span class="go"> [rustsbi] Platform SMP : 1</span>
|
||
<span class="go"> [rustsbi] Platform Memory : 0x80000000..0x88000000</span>
|
||
<span class="go"> [rustsbi] Boot HART : 0</span>
|
||
<span class="go"> [rustsbi] Device Tree Region : 0x87000000..0x87000ef2</span>
|
||
<span class="go"> [rustsbi] Firmware Address : 0x80000000</span>
|
||
<span class="go"> [rustsbi] Supervisor Address : 0x80200000</span>
|
||
<span class="go"> [rustsbi] pmp01: 0x00000000..0x80000000 (-wr)</span>
|
||
<span class="go"> [rustsbi] pmp02: 0x80000000..0x80200000 (---)</span>
|
||
<span class="go"> [rustsbi] pmp03: 0x80200000..0x88000000 (xwr)</span>
|
||
<span class="go"> ......</span>
|
||
<span class="go"> [PASS] found <current time_msec = (\d+)></span>
|
||
<span class="go"> [PASS] found <Test wait OK42266!></span>
|
||
<span class="go"> [PASS] found <time_msec = (\d+) after sleeping (\d+) ticks, delta = (\d+)ms!></span>
|
||
<span class="go"> [PASS] found <Test 04_4 test OK42266!></span>
|
||
<span class="go"> [PASS] found <Test 04_6 ummap2 OK42266!></span>
|
||
<span class="go">......</span>
|
||
<span class="go"> [PASS] found <Test set_priority OK42266!></span>
|
||
<span class="go"> [PASS] found <Test write B OK42266!></span>
|
||
<span class="go"> [PASS] not found <FAIL: T.T></span>
|
||
<span class="go"> [PASS] not found <Should cause error, Test 04_2 fail!></span>
|
||
<span class="go"> [PASS] not found <Should cause error, Test 04_3 fail!></span>
|
||
|
||
<span class="go"> Test passed42266: 24/24</span>
|
||
|
||
<span class="go"> stride ratio = [15202320, 13745266, 13849200, 12149100, 10944222, 9782240]</span>
|
||
<span class="go"> [PASS] Stride Test</span>
|
||
|
||
<span class="go"> Test passed42266: 1/1</span>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
<ul>
|
||
<li><p>提交你的修改</p>
|
||
<blockquote>
|
||
<div><ul class="simple">
|
||
<li><p>如果是基于GitHub Classroom 开发, 在本地环境或在线codespaces环境下，执行 <code class="docutils literal notranslate"><span class="pre">git</span> <span class="pre">push</span></code> 命令，提交修改的代码到gitub进行CI自动评测。如果评测结果是 红色小叉 （位于repo的中上位置），可进一步点击红色小叉查找具体出错时的CI执行情况。</p></li>
|
||
</ul>
|
||
</div></blockquote>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id3">
|
||
<h2>问答作业<a class="headerlink" href="#id3" title="永久链接至标题">¶</a></h2>
|
||
<p>stride 算法深入</p>
|
||
<blockquote>
|
||
<div><p>stride 算法原理非常简单，但是有一个比较大的问题。例如两个 stride = 10 的进程，使用 8bit 无符号整形储存
|
||
pass， p1.pass = 255, p2.pass = 250，在 p2 执行一个时间片后，理论上下一次应该 p1 执行。</p>
|
||
<ul class="simple">
|
||
<li><p>实际情况是轮到 p1 执行吗？为什么？</p></li>
|
||
</ul>
|
||
<p>我们之前要求进程优先级 >= 2 其实就是为了解决这个问题。可以证明， <strong>在不考虑溢出的情况下</strong> , 在进程优先级全部 >= 2
|
||
的情况下，如果严格按照算法执行，那么 PASS_MAX – PASS_MIN <= BigStride / 2。</p>
|
||
<ul class="simple">
|
||
<li><p>为什么？尝试简单说明（不要求严格证明）。</p></li>
|
||
<li><p>已知以上结论，<strong>考虑溢出的情况下</strong>，可以为 pass 设计特别的比较器，让 BinaryHeap<Pass> 的 pop
|
||
方法能返回真正最小的 Pass。补全下列代码中的 <code class="docutils literal notranslate"><span class="pre">partial_cmp</span></code> 函数，假设两个 Pass 永远不会相等。</p></li>
|
||
</ul>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="k">use</span><span class="w"> </span><span class="n">core</span>::<span class="n">cmp</span>::<span class="n">Ordering</span><span class="p">;</span><span class="w"></span>
|
||
|
||
<span class="k">struct</span> <span class="nc">Pass</span><span class="p">(</span><span class="kt">u64</span><span class="p">);</span><span class="w"></span>
|
||
|
||
<span class="k">impl</span><span class="w"> </span><span class="nb">PartialOrd</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">Pass</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">fn</span> <span class="nf">partial_cmp</span><span class="p">(</span><span class="o">&</span><span class="bp">self</span><span class="p">,</span><span class="w"> </span><span class="n">other</span>: <span class="kp">&</span><span class="nc">Self</span><span class="p">)</span><span class="w"> </span>-> <span class="nb">Option</span><span class="o"><</span><span class="n">Ordering</span><span class="o">></span><span class="w"> </span><span class="p">{</span><span class="w"></span>
|
||
<span class="w"> </span><span class="c1">// ...</span>
|
||
<span class="w"> </span><span class="p">}</span><span class="w"></span>
|
||
<span class="p">}</span><span class="w"></span>
|
||
|
||
<span class="k">impl</span><span class="w"> </span><span class="nb">PartialEq</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">Pass</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">fn</span> <span class="nf">eq</span><span class="p">(</span><span class="o">&</span><span class="bp">self</span><span class="p">,</span><span class="w"> </span><span class="n">other</span>: <span class="kp">&</span><span class="nc">Self</span><span class="p">)</span><span class="w"> </span>-> <span class="kt">bool</span> <span class="p">{</span><span class="w"></span>
|
||
<span class="w"> </span><span class="kc">false</span><span class="w"></span>
|
||
<span class="w"> </span><span class="p">}</span><span class="w"></span>
|
||
<span class="p">}</span><span class="w"></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>TIPS: 使用 8 bits 存储 pass, BigStride = 255, 则: <code class="docutils literal notranslate"><span class="pre">(125</span> <span class="pre"><</span> <span class="pre">255)</span> <span class="pre">==</span> <span class="pre">false</span></code>, <code class="docutils literal notranslate"><span class="pre">(129</span> <span class="pre"><</span> <span class="pre">255)</span> <span class="pre">==</span> <span class="pre">true</span></code>.</p>
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||
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