COTS Moves to Multicore: COTS Moves to Multicore: Software Considerations to Ease the Transition To Multi-coreChris Ault, Senior Product Manager – Wind River

Evolution to Multi-core

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Migrating from Single-Core to Multi-core

� Performance:– There may be increases

– There may be decreases• Data dependencies

• Race conditions

� Programming Model– Revisit your synchronization assumptions

– There is shared hardware in there!

� Algorithms: need to be multi-core-aware

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Migrating from Single-Core to Multi-core

� Shared hardware on the board

� OS privilege levels: multiple instances of the kernel, one per core

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Multi-core: Shared Hardware Resources

� All cores share access to– I/O devices

– Memory

– Timers/clocks

– Interrupt controller

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Core Core Core Core

IDE Ethernet MemoryTimer Serial

Interrupt Controller

Privilege Modes: Single-Core

Operating systems work in privilege modes:� The OS kernel itself can do anything with the hardware

� Device drivers are more restricted

� User applications/components are least privileged

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Intel privilege rings source: Wikipedia

Ring 3

Ring 2

Ring 1

Ring 0

Kernel

Device Drivers

Device Drivers

Applications

Least Privileged

Most Privileged

Example based on Intel privilege rings, other processors have similar concepts

AM

P

Privilege Modes and Multi-core

� Cores in privilege mode can control the entire hardware and mask interrupts

� More control may be required in a multi-core setting

� Can seriously impacts robustness

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Ring 3Ring 2Ring 1

Ring 0

Kernel

Device Drivers

Device Drivers

Applications

Ring 3Ring 2Ring 1

Ring 0

Kernel

Device Drivers

Device Drivers

Applications

Ring 3Ring 2Ring 1

Ring 0

Kernel

Device Drivers

Device Drivers

Applications

Ring 3Ring 2Ring 1

Ring 0

Kernel

Device Drivers

Device Drivers

Applications

Core Core Core Core

SM

P

SMP Operating System

� Multiple instances of tasks running at the same priority

� Lower priority tasks running concurrently with higher priority tasks

� Lower priority tasks may mask interrupts and starve higher priority tasks

Review Your Assumptions

higher priority tasks

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Algorithms, Data Parallelism

� Traditional Single-core systems:– Single instance of processing task operates on complete data

set

– Does not utilize all cpu cores

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Core

Core

Core

Core

DataProcessing

Data Set

Idle

cor

es

Data Parallelism

� Multiple instances of data processing, operating on smaller subsets of data

� Multi-core-aware algorithms are necessary to realize increases in processing speed

– Re-architect & re-write code

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Core

Core

Core

Core

Data Processing

Data Subsets

Data Processing

Data Processing

Data Processing

Complex Challenges When Migrating To Multi-core

� Shared hardware on the board– I/O devices, memory, interrupt controller

� Non-parallel code needs to be re-written, re-testedtested

� OS privilege levels: multiple instances of the kernel, one per core

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It’s Not All That Gloomy ….

With Embedded Virtualization …..

� Virtualize accesses to shared hardware

– Shared access is controlled outside of your app

– Interrupt controller, memory regions, devices

� Retain execution behavior of existing apps

– Minimize retesting/rewriting

� Add new functionality on remaining cores

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Apps

OS

Core 1

Apps

Core 2

OS

Hypervisor

Apps Apps