1. Questions To Ask When Considering Designing Asymmetric Multiprocessing Systems
George Cox

2. Agenda Context of Asymmetric Multiprocessing Systems design
Including Asymmetric Multicore Systems
Closeness
Sharing – tight to loose, up the semantics stack
Communication overheads – tight to loose physical connection
Closer => less latency => less overheads =>
Better performance?
Lower power?
Integrating New Functionality
Continuing new types
Natural tendency to want to integrate support to improve
Performance
Power
Cost
Competitiveness

3. Context Asymmetric Multiprocessing Systems
Including Asymmetric Multicore Systems
You have a multi-dimensional space in which to work
We will describe a two (2) space example
You must pick the optimal(?) point(s) within your design constraints
You rarely get a “clean sheet of paper”
Historical I/O models – driver-based, “through” data flow
Historical coprocessor models – driver-based, “in and back out” data flow

4. Sharing Equivalent shared semantics Between processing elements
Up the semantics stack
Physical addressing – size, shared or separated, movement between
Logical addressing – address translation (e.g., paging)
Virtual addressing – uniform (or not) swapping model
Caching – same number of levels, line length, sizes, replacement algorithms, consistency model, inter-core/processor handshakes
Processing element functionality
Same ISA (or not)
Virtual machines – uniform semantics, representation, migration across ISA/performance differences

5. Communication Overheads
Tight to loose physical connection – less to more latency
Intra-die
Inter-die
Inter-package
Shared memory
Via bus
Via network

6. Design Space Sharing Virtual Addressing Physical Addressing
Logical Addressing
Caching
Processing Element Functionality
Virtual Machines
Better?
Worse?
Intra-Die
Inter-Die
Inter Package
Shared Memory
Via Bus
Via Network
Communication Overheads

7. Integrating New Functionality
New types
Cryptography, graphics, radios, sensors
Granularity
Which kind of interface to use
Instruction
Accelerator(s) - ISA (synchronous or asynchronous) interface
I/O – driver (asynchronous) interface
Coprocessor – driver (asynchronous) interface
Sequencing
Synchronous
Long running functions can pose response latency for OS;
Divide function into sequence of smaller functions (e.g., AESNI)
Asynchronous – fork, join
In the end
We have tried lots of kinds of interfaces over time
Instructions (almost always eventually) win