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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<concept id="GUID-387E98B0-568D-4DBB-9A9E-616E41E96B58" xml:lang="en"><title>SMP
+Overview</title><shortdesc>This document introduces Symmetric Multiprocessing (SMP) on the
+Symbian platform.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<section id="GUID-105AFE3B-F000-4548-B57E-4A5EAEBA2645"><title>Purpose</title> 
+     <p>An SMP operating system enables any CPU to work on any task, enabling
+multiple threads (processes or multiple threads within a process, and therefore
+applications) to run in parallel. </p><p>A system with 2 CPUs, for example,
+can allow 2 threads to run concurrently; one on each processor. This provides
+better responsiveness and asynchronicity compared to a system with a single
+CPU.</p><p>An SMP system can deliver a similar level of CPU performance as
+a larger and faster uni-processor CPU, while using less power. SMP also provides
+additional power management flexibility, running a single CPU when the system
+is under utilised then switching on extra CPUs to give scalable performance
+on demand for media rich applications. The ARM SMP architecture allows power
+control with voltage / frequency scaling and the ability to switch individual
+cores on and off.</p><p>However, the benefits of SMP come at the cost of OS
+and application complexity (the requirement of extra locks and the multithreading
+of code) and the associated debugging challenges of parallel processing.</p> 
+   </section>
+<section id="GUID-38C8CACC-0CCD-460B-9713-B33FF79FE75B"><title>Description</title><p>SMP
+is a microprocessor architecture where two or more identical CPUs are connected
+to a single shared main memory system and run a single OS instance. </p><p>The
+diagram below shows how this would apply on the Symbian platform with four
+CPU cores. <fig id="GUID-FBBCE840-E295-4287-BA10-DF37292D432B">
+<title>The Simplified Architecture of an SMP Platform Executing on the Symbian
+Platform.  </title>
+<image href="GUID-85A84BAA-4FA2-4A26-A8B1-57018D8838C3_d0e638374_href.jpg" placement="inline"/>
+</fig></p><p>The figure shows a simplified block diagram of an SMP system,
+where 4 CPUs are connected through their own cache to shared RAM and peripherals.
+The Cache Coherency Control block is responsible for ensuring that each CPU
+cache is consistent with those of the other CPUs. A single instance of OS
+spans the CPUs, the scheduler decides which thread to execute next and upon
+which CPU it should execute. </p></section>
+<section id="GUID-1672A908-7BE6-4261-997B-2495C598A6E0"><title>SMP features</title><p>The
+features of the SMP platform are: <ul>
+<li><p><b>Better responsiveness</b></p><p>One or more CPU cores can be dedicated
+to IO related work. </p></li>
+<li><p><b>High performance on demand</b></p><p>Work can be moved onto CPUs
+when required. </p></li>
+<li><p><b>Flexible power management</b></p><p> CPU cores can be switched on
+or off, or voltage/frequency scaled, according to the current processing requirements
+of the system.</p><p>This can lead to improved battery life because the system
+only uses as much processing power as required at any given time.</p></li>
+<li><p><b>Scalable architecture</b></p><p>SMP can work over two or more CPU
+cores. </p></li>
+</ul></p></section>
+<section id="GUID-D4A04CA3-2E37-4DE1-BF98-C08365F8DFB0"><title>SMP limitations</title><p>The
+disadvantages of using SMP are: </p><ul>
+<li><p><b>The original emulator for the Symbian platform will not emulate
+an SMP environment</b></p><p>The emulator is being replaced by a new emulation
+environment that is capable of simulating the multiprocessor environment.</p></li>
+<li><p><b>Software changes are required</b></p><p>Assumptions that can be
+made in a single core environment, are not necessarily true on a multi-core
+system. The SMP-safe documentation you are reading now will provide you with
+guidance on a number of issues sure to come up while migrating your software
+to work in an SMP environment.</p></li>
+<li><p><b>Debugging Challenges</b></p><p>Debugging on a multi-processor system
+is extremely difficult. The standard tooling solutions, such as the Lauterbach
+debugger and BTrace2 (also known as the modified BTrace) have been revised
+to handle the special requirements of an SMP system.</p></li>
+<li><p><b>Access to memory is serialized</b></p><p>All the CPU cores use the
+same memory, memory access must occur serially. This can cause a performance
+lag. </p></li>
+</ul></section>
+</conbody><related-links>
+<link href="GUID-242D9F27-401B-4230-B3A6-11E2D9D3DE17.dita"><linktext>SMP - Threading
+Model</linktext></link>
+<link href="GUID-16AED228-539F-4BF7-A7FD-9A01FF1A9A84.dita"><linktext>SMP - Locking</linktext>
+</link>
+<link href="GUID-9D93F895-B975-4F2D-A2A3-817033EA5C12.dita"><linktext>SMP - Data
+Integrity and memory barriers</linktext></link>
+<link href="GUID-A3647D6A-4B5E-4A31-8A53-AC822E669AB6.dita"><linktext>SMP - SMP
+Scheduling</linktext></link>
+<link href="GUID-821C254A-40C6-45F9-B2F9-2CF28CAEB8CC.dita"><linktext>SMP - Interrupt
+Handling</linktext></link>
+<link href="GUID-734588CA-5644-438A-9CC9-77ECBE0C1EEA.dita"><linktext>SMP - Obsolete
+Mechanisms</linktext></link>
+<link href="GUID-EE019780-130A-4469-924D-E83D74C2ABE5.dita"><linktext>SMP - Building
+For An SMP Platform</linktext></link>
+<link href="GUID-F44ED3DD-F74F-4C79-8E56-1CBBCCA90C91.dita"><linktext>SMP - Porting
+Guide</linktext></link>
+<link href="GUID-6B8B45E5-1594-455E-9FAE-0A7768305F95.dita"><linktext>SMP - Development
+Tips For Making Code SMP Safe</linktext></link>
+<link href="GUID-C8E61F9D-54E7-4B93-9726-6E96D79334F9.dita"><linktext>SMP - Hardware
+Platforms</linktext></link>
+<link href="GUID-F23E0D38-65C2-40B9-AC19-F5AEBBEB2E82.dita"><linktext>SMP - Debugging
+In An SMP Environment</linktext></link>
+<link href="GUID-23BD6377-CE67-46CC-8311-D40D34BCFB6A.dita"><linktext>SMP - Tutorial
+Overview</linktext></link>
+</related-links></concept>
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