1. Some challenges in heterogeneous multi-core systems
Capstone - Fall 2012
Some challenges in heterogeneous multi-core systems

2. Multi-core system evolution
Big core
Big core
Big core
Big core
Big core
Big core
Small core
Small core
Small core
Small core
Small core
Small core
Small core
Small core
Traditional homogenous multi-core system
Asymmetric/heterogeneous multi-core system

3. Heterogeneous platform
Thread
Big core
Big core
Thread
Thread
Small core
Small core
Small core
Small core
. . .
Small core
Small core
Small core
Small core
Thread
Compute-intensive vs memory/IO-intensive threads
Single-ISA high-performance "big” vs low-power "small” types of cores

4. Challenges Big core Big core
Characterization of thread behavior when running on different core types: is it CPU-bound or memory-bound? Or something else altogether?
Optimized thread allocation on the different core types
Thread allocation/scheduling within each core type
Big core
Big core ?
Thread ?
Small core
Small core
Small core
Small core
Small core
Small core
Small core
Small core

5. Characterizing thread behavior
Monitor thread performance, measuring counters
Cache misses
Number of instructions per cycle
Predict thread performance in “the other” core type
Cores differing in clock speed/frequency
Cores differing in micro-architectural characteristics (in-order vs out-of-order)
Does big/small core bias influence speed up of threads?
Contention in shared resources (cache/memory)
Bottleneck identification in multithreaded apps
Threads likely on critical path
Context switches, cache pollution, hyperthreading?

6. Scheduling threads to cores
Power and performance trade-off
Big core consumes more power but shorten execution time
Energy = Power x Time
Real-time/performance guarantees
Latency-sensitive apps
Fairness
Avoid big core monopolization
Power/energy reduction
Explicitly account for core power consumption
Thread consolidation in few cores as possible
power off unused cores
energy savings vs. performance degradation (resource contention)
Acceleration of critical path in multithreaded apps
HPC apps