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   </ul>
 </div>
 
+<div class="slide">
+  <h1>Network busy-polling [3.11] (1)</h1>
+  <p>A conventional network request/response process looks like:</p>
+  <small><!-- ew -->
+    <ol class="incremental">
+      <li>
+	Task calls <tt>send()</tt>; network stack constructs a
+	packet; driver adds it to hardware Tx queue
+      </li>
+      <li>
+	Task calls <tt>poll()</tt> or <tt>recv()</tt>, which blocks;
+	kernel puts it to sleep and possibly idles the CPU
+      </li>
+      <li>
+	Network adapter receives response and generates IRQ, waking
+	up CPU
+      </li>
+      <li>
+	Driver's IRQ handler schedules polling of the hardware Rx
+	queue (NAPI)
+      </li>
+      <li>
+	Kernel runs the driver's NAPI poll function, which passes
+	the response packet into the network stack
+      </li>
+      <li>
+	Network stack decodes packet headers and adds packet to
+	the task's socket
+      </li>
+      <li>
+	Network stack wakes up sleeping task; scheduler switches
+	to it and the socket call returns
+      </li>
+    </ol>
+  </small>
+</div>
+
+<div class="slide">
+  <h1>Network busy-polling [3.11] (2)</h1>
+  <ul class="incremental">
+    <li>
+      If driver supports busy-polling, it tags each packet with
+      the receiving NAPI context, and kernel tags sockets
+    </li>
+    <li>
+      When busy-polling is enabled, <tt>poll()</tt>
+      and <tt>recv()</tt> call the driver's busy poll function to
+      check for packets synchronously (up to some time limit)
+    </li>
+    <li>
+      If the response usually arrives quickly, this reduces overall
+      request/response latency as there are no context switches and
+      power transitions
+    </li>
+    <li>
+      Time limit set by sysctl (<tt>net.busy_poll</tt>,
+      <tt>net.busy_read</tt>) or socket option (<tt>SOL_SOCKET,
+      SO_BUSY_POLL</tt>); requires tuning
+    </li>
+  </ul>
+</div>
+
 <div class="slide">
   <h1>Questions?</h1>
 </div>