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    <li>Add Kernels for a New Device</li>
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  <div class="section" id="add-kernels-for-a-new-device">
<span id="add-kernels-for-a-new-device"></span><h1>Add Kernels for a New Device<a class="headerlink" href="#add-kernels-for-a-new-device" title="Permalink to this headline">¶</a></h1>
<div class="section" id="background">
<span id="background"></span><h2>Background<a class="headerlink" href="#background" title="Permalink to this headline">¶</a></h2>
<p>PaddlePaddle Fluid have hundreds of operators.  Each operator could have one or more kernels.  A kernel is an implementation of the operator for a certain device, which could be a hardware device, e.g., the CUDA GPU, or a library that utilizes a device, e.g., Intel MKL that makes full use of the Xeon CPU.</p>
<p><a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/doc/howto/dev/new_op_en.md">This document</a> explains how to add an operator, and its kernels.  The kernels of an operator are indexed by a C++ type <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/doc/design/operator_kernel_type.md"><code class="docutils literal"><span class="pre">OpKernelType</span></code></a>.  An operator chooses the right kernel at runtime.  This choosing mechanism is described <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/doc/design/switch_kernel.md">here</a>.</p>
</div>
<div class="section" id="write-kernels-for-a-new-device">
<span id="write-kernels-for-a-new-device"></span><h2>Write Kernels for A New Device<a class="headerlink" href="#write-kernels-for-a-new-device" title="Permalink to this headline">¶</a></h2>
<div class="section" id="add-a-new-device">
<span id="add-a-new-device"></span><h3>Add A New Device<a class="headerlink" href="#add-a-new-device" title="Permalink to this headline">¶</a></h3>
<p>For some historical reaons, we misuse the word <em>library</em> for <em>device</em>.  For example, we call the deivce type by <em>library type</em>.  An example is the header file <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/framework/library_type.h#L24"><code class="docutils literal"><span class="pre">library_type.h</span></code></a>.  We will correct this ASAP.</p>
<p>To register a new device, we need to add an enum value to <code class="docutils literal"><span class="pre">LibraryType</span></code>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">enum</span> <span class="k">class</span> <span class="nc">LibraryType</span> <span class="p">{</span>
  <span class="n">kPlain</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span>
  <span class="n">kMKLDNN</span> <span class="o">=</span> <span class="mi">1</span><span class="p">,</span>
  <span class="n">kCUDNN</span> <span class="o">=</span> <span class="mi">2</span><span class="p">,</span>
<span class="p">};</span>
</pre></div>
</div>
</div>
<div class="section" id="add-a-new-place">
<span id="add-a-new-place"></span><h3>Add A New <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/platform/place.h#L53">Place</a><a class="headerlink" href="#add-a-new-place" title="Permalink to this headline">¶</a></h3>
<p>If you have a new kind of Device, firstly you need to add a new kind of <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/platform/place.h#L53"><code class="docutils literal"><span class="pre">Place</span></code></a>. For example <code class="docutils literal"><span class="pre">CUDAPlace</span></code>:</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="k">struct</span> <span class="n">CUDAPlace</span> <span class="p">{</span>
  <span class="n">CUDAPlace</span><span class="p">()</span> <span class="o">:</span> <span class="n">CUDAPlace</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="p">{}</span>
  <span class="k">explicit</span> <span class="n">CUDAPlace</span><span class="p">(</span><span class="kt">int</span> <span class="n">d</span><span class="p">)</span> <span class="o">:</span> <span class="n">device</span><span class="p">(</span><span class="n">d</span><span class="p">)</span> <span class="p">{}</span>

  <span class="kr">inline</span> <span class="kt">int</span> <span class="n">GetDeviceId</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">device</span><span class="p">;</span> <span class="p">}</span>
  <span class="c1">// needed for variant equality comparison</span>
  <span class="kr">inline</span> <span class="kt">bool</span> <span class="k">operator</span><span class="o">==</span><span class="p">(</span><span class="k">const</span> <span class="n">CUDAPlace</span> <span class="o">&amp;</span><span class="n">o</span><span class="p">)</span> <span class="k">const</span> <span class="p">{</span>
    <span class="k">return</span> <span class="n">device</span> <span class="o">==</span> <span class="n">o</span><span class="p">.</span><span class="n">device</span><span class="p">;</span>
  <span class="p">}</span>
  <span class="kr">inline</span> <span class="kt">bool</span> <span class="k">operator</span><span class="o">!=</span><span class="p">(</span><span class="k">const</span> <span class="n">CUDAPlace</span> <span class="o">&amp;</span><span class="n">o</span><span class="p">)</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="o">!</span><span class="p">(</span><span class="o">*</span><span class="k">this</span> <span class="o">==</span> <span class="n">o</span><span class="p">);</span> <span class="p">}</span>

  <span class="kt">int</span> <span class="n">device</span><span class="p">;</span>
<span class="p">};</span>

<span class="k">typedef</span> <span class="n">boost</span><span class="o">::</span><span class="n">variant</span><span class="o">&lt;</span><span class="n">CUDAPlace</span><span class="p">,</span> <span class="n">CPUPlace</span><span class="o">&gt;</span> <span class="n">Place</span><span class="p">;</span>
</pre></div>
</div>
</div>
<div class="section" id="add-device-context">
<span id="add-device-context"></span><h3>Add <a class="reference external" href="(https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/platform/device_context.h#L37)">device context</a><a class="headerlink" href="#add-device-context" title="Permalink to this headline">¶</a></h3>
<p>After a new kind of Device is added, you should add a corresponding <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/platform/device_context.h#L37">DeviceContext</a> for it.</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">DeviceContext</span> <span class="p">{</span>
 <span class="k">public</span><span class="o">:</span>
  <span class="k">virtual</span> <span class="o">~</span><span class="n">DeviceContext</span><span class="p">()</span> <span class="p">{}</span>
  <span class="k">virtual</span> <span class="n">Place</span> <span class="n">GetPlace</span><span class="p">()</span> <span class="k">const</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>

  <span class="k">virtual</span> <span class="kt">void</span> <span class="nf">Wait</span><span class="p">()</span> <span class="k">const</span> <span class="p">{}</span>
<span class="p">};</span>
</pre></div>
</div>
</div>
<div class="section" id="implement-new-opkernel-for-your-device">
<span id="implement-new-opkernel-for-your-device"></span><h3>Implement new <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/framework/operator.h#L351">OpKernel</a> for your Device.<a class="headerlink" href="#implement-new-opkernel-for-your-device" title="Permalink to this headline">¶</a></h3>
<p>A detailed documentation can be found in <a class="reference external" href="https://github.com/PaddlePaddle/Paddle/blob/develop/doc/howto/dev/new_op_en.md"><code class="docutils literal"><span class="pre">new_op_and_kernel</span></code></a></p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">OpKernelBase</span> <span class="p">{</span>
 <span class="k">public</span><span class="o">:</span>
  <span class="cm">/**</span>
<span class="cm">   * ExecutionContext is the only parameter of Kernel Run function.</span>
<span class="cm">   * Run will get input/output variables, state such as momentum and</span>
<span class="cm">   * device resource such as CUDA stream, cublas handle, etc. from</span>
<span class="cm">   * ExecutionContext. User should construct it before run the Operator.</span>
<span class="cm">   */</span>

  <span class="k">virtual</span> <span class="kt">void</span> <span class="n">Compute</span><span class="p">(</span><span class="k">const</span> <span class="n">ExecutionContext</span><span class="o">&amp;</span> <span class="n">context</span><span class="p">)</span> <span class="k">const</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>

  <span class="k">virtual</span> <span class="o">~</span><span class="n">OpKernelBase</span><span class="p">()</span> <span class="o">=</span> <span class="k">default</span><span class="p">;</span>
<span class="p">};</span>

<span class="k">template</span> <span class="o">&lt;</span><span class="k">typename</span> <span class="n">T</span><span class="o">&gt;</span>
<span class="k">class</span> <span class="nc">OpKernel</span> <span class="o">:</span> <span class="k">public</span> <span class="n">OpKernelBase</span> <span class="p">{</span>
 <span class="k">public</span><span class="o">:</span>
  <span class="k">using</span> <span class="n">ELEMENT_TYPE</span> <span class="o">=</span> <span class="n">T</span><span class="p">;</span>
<span class="p">};</span>
</pre></div>
</div>
</div>
<div class="section" id="register-the-opkernel-to-framework">
<span id="register-the-opkernel-to-framework"></span><h3>Register the OpKernel to framework<a class="headerlink" href="#register-the-opkernel-to-framework" title="Permalink to this headline">¶</a></h3>
<p>After writing the components described above, we should register the kernel to the framework.</p>
<p>We use <code class="docutils literal"><span class="pre">REGISTER_OP_KERNEL</span></code> to do the registration.</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="n">REGISTER_OP_KERNEL</span><span class="p">(</span>
    <span class="n">op_type</span><span class="p">,</span>
    <span class="n">library_type</span><span class="p">,</span>
    <span class="n">place_type</span><span class="p">,</span>
    <span class="n">kernel0</span><span class="p">,</span> <span class="n">kernel1</span><span class="p">,</span> <span class="p">...)</span>
</pre></div>
</div>
<p>kernel0, kernel1 are kernels that have the same <code class="docutils literal"><span class="pre">op_type</span></code>, <code class="docutils literal"><span class="pre">library_type</span></code>, <code class="docutils literal"><span class="pre">place_type</span></code> but different <code class="docutils literal"><span class="pre">data_types</span></code>.</p>
<p>take <a class="reference external" href="(https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/operators/conv_cudnn_op.cu.cc#L318)"><code class="docutils literal"><span class="pre">conv2d</span></code></a> as an example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span>```cpp
REGISTER_OP_KERNEL(conv2d, CPU, paddle::platform::CPUPlace,
        paddle::operators::GemmConvKernel&lt;paddle::platform::CPUDeviceContext, float&gt;,
        paddle::operators::GemmConvKernel&lt;paddle::platform::CPUDeviceContext, double&gt;);

REGISTER_OP_KERNEL(conv2d, CUDNN, ::paddle::platform::CUDAPlace,
       paddle::operators::CUDNNConvOpKernel&lt;float&gt;,
       paddle::operators::CUDNNConvOpKernel&lt;double&gt;);
```
</pre></div>
</div>
<p>In the code above:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">conv2d</span></code> is the type/name of the operator</li>
<li><code class="docutils literal"><span class="pre">CUDNN/CPU</span></code> is <code class="docutils literal"><span class="pre">library</span></code></li>
<li><code class="docutils literal"><span class="pre">paddle::platform::CUDAPlace/CPUPlace</span></code> is <code class="docutils literal"><span class="pre">place</span></code></li>
<li>template parameter <code class="docutils literal"><span class="pre">float/double</span></code> on <code class="docutils literal"><span class="pre">CUDNNConvOpKernel&lt;T&gt;</span></code> is <code class="docutils literal"><span class="pre">data_type</span></code>.</li>
</ul>
</div>
</div>
</div>


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