Heterogeneous Multi-processor
A. Classic design Flow
The software design use programming models to abstract the hardware architecture.
Figure 1 Classic design flow
To produce efficient code, the software needs to be adapted to the target architecture by using
specific libraries, such as system library for the different hardware components or specific
memory mapping for the different CPU and memory architectures. Discontinuities in the
software design, i.e. the software compiler ignores the processor architecture (e.g. interrupts or
specific I/Os).
Figure 2 execution
The combination of the platform with the software code produces an executable model that
emulates the execution of the final system, including hardware and software architecture. This
executable model allows simulation of the software with detailed hardware–software interaction,
software debug, and eventually performance measurement.
B. Ideal Design Flow
The ideal scheme would be able to produce an efficient software code starting from a high-level
program using generic communication primitives, such as send/recv. In an ideal design flow, the
software generation targeting a specific architecture consists of partitioning and mapping, final
application software code generation and hardware dependent software (HDS) code generation.
Figure 3 ideal design flow
The HdS is made of lower software layers that may incorporate an operating system (OS),
communication management, and a hardware abstraction layer to allow the OS functions to
access the hardware resources of the platform. Unfortunately, we are still missing such an ideal
generic flow, able to efficiently map high-level programs on heterogeneous MPSoC
architectures. In addition, the validation and debugging of HdS remains the main bottleneck in
MPSoC design because each processor subsystem requires specific HdS implementation to be
efficient.
1. Software oriented
The software-oriented approaches make use of a software model in the form of a runtime library
to model the interaction with the hardware. The application can be written in a high-level
language. The software stack construction consists of compiling this code and linking the results
with the run-time libraries. The software stack construction consists of compiling this code and
linking the results with the run-time libraries. The library is defined separately for each processor
and can be very sophisticated.
2. Hardware oriented
The hardware-oriented approach executes the final software on a virtual platform and it
corresponds to classic hardware–software co-simulation models using instruction-set simulators
(ISS). These techniques require that all the software and hardware are fully specified..
3. Electronic system level (ESL) design-oriented
The ESL oriented approaches use high-level APIs (application programming interface) to
abstract the hardware software interfaces. This approach enables the automatic generation of a
virtual prototype from a system-level model, but the generation of HdS software layer is
performed in one step, which generally implies the use of predefined communication schemes.
Summary of Heterogeneous Multi-Processing
 A heterogeneous system provides the diverse instruction set architectures which allow entire
computing environments (operating systems and application bases) to be incorporated into a
M P system. The best that homogeneous systems can offer is to extend the power of a single
computing environment, which does not extend the fundamental instruction set (and hence
the software application base) of the system.
 It is commonly accepted that software is currently the gating factor in computer system
evolution. Software technology is lagging far behind hardware technology. To address this
issue the heterogeneous multiprocessing system encourages hardware to be ported in addition
to software. This hardware porting creates exciting new avenues for computer system
expansion.
 An object-oriented approach was used in defining the HMW. The information hiding nature
of an object-based approach prevents the underlying code and data differences of
heterogeneous processing elements from interfering with system-level design. Objectoriented approach to unify the heterogeneous system.
 Processes are heterogeneous and capable of running under different operating systems ·with
dynamic mobility supported. Heterogeneous, mobile processes enhance flexibility and
performance.
 A set of system primitives was defined to assist in the management of objects and processes.
The primitives are presented as model constructs for language extension. Consider
multiprocessor platforms in which only programmable processors are used as processing
components, and they communicate data only through distributed memory units.
 A "programmer friendly" development environment is sure to produce better software faster
than a hostile system which gives up debugging information begrudgingly. The complexity
of Multi-Processer design, coupled with the added problems of heterogeneous systems such
as data format differences, demands development tools integrated into the computer at the
system level.
Heterogeneous MP Scheduling


In simple MP are self-scheduled It means that there is no need for a global scheduler
component in platforms. The processors in platforms can be connected either by a
crossbar switch (CBS), or a P2P network, or a shared bus (ShB).
Heterogeneous multi-cores are typically composed of small and big cores using global
scheduler. Global Scheduler parses each service request and accordingly it interacts with
the rest of the platform through the Cloud Database (DB). For different core types on a
single die has the potential to improve energy-effiency without sacrificing significant
performance. However, the success of heterogeneous multi-cores is directly dependent on
how well a scheduling policy maps workloads to the best core type (big or small).
Incorrect scheduling decisions can unnecessarily degrade performance and waste
energy/power.
Advantages and Disadvantages of Heterogeneous Multi-Processors
Advantage
Disadvantage
Increased reliability
Increased software complexity
Increased survivability
Difficult system test and failure
diagnosis
Increased processing power
Unique expertise for
design/development required
Increased responsiveness
Bus arbitration required
Higher degree of modularity
System expandability in smaller
Increments
Table 1
Today’s Use
1. XBOX 360
Figure 4 Xbox
Specifications
3 CPU cores
– 4-way SIMD vector units
– 8-way 1MB L2 cache (3.2 GHz)
– 2 way SMT
– In-order 2 Instructions/cycle
• ATI GPU with embedded EDRAM
• 3D graphics units
• 512-Mbyte DRAM main memory
• Big performance increase over last generation
• Support high-definition video
• Extremely high pixel fill rate (goal: 100+ million pixels/s)
• Flexible to suit dynamic range of games
• balance hardware, homogenous resources
• Programmability (easy to program)
2. Cell Processor
Each cell chip has:
•One power PC Core 8 computer cores
•One chip memory controllers
•One chip I/O
•One chip network to connect them all
Figure 5 cell processor
Heterogeneous computing platforms can be found in every domain of computing—from
high-end servers and high-performance computing machines all the way down to low
power embedded devices including mobile phones and tablets.
Multiprocessor
Objectives
Multiprocessor systems
Why build multiprocessor systems
Problems
Solutions
Heterogeneity