1. Migration Cost Aware Task Scheduling 18-743 Milestone Shraddha Joshi, Brian Osbun 10/24/2013

2. Outline Problem description Approach Milestone I Methodology Results Observations Future Work 2

3. Problem Description Dynamic schedulers allow task migration during program execution Migrating threads to new cores can have hidden costs  Cold cache misses  Overhead of moving architectural state  Congestion on interconnect during transfer Most task schedulers ignore migration overhead Problem statement: quantify and consider the task migration cost when evaluating scheduling possibilities 3

4. Approach Architectural transfer is essentially fixed cost  Can be modeled independently Cache effects have a larger and variable cost Published theory requires static analysis*  Determination of “useful” blocks in cache  Reaching memory blocks (RMB): all blocks that may be in cache at a point  Live memory blocks (LMB): all blocks that may be referenced before eviction  Usefulness is intersection of RMB and LMB Dynamic analysis  Need prediction!  For now: everything’s useful! *Source-Hardy et. al. Estimation of Cache Related Migration Delays for Multi-Core Processors with Shared Instruction Caches 4

5. Milestone I To be able to quantify migration cost in terms of a metric  Our predictor: past cache accesses  Our prediction: future cache misses 5

6. Methodology Sniper simulation framework Clustered architecture  Homogeneous cores  Clustered L1 caches (shared by 4 cores)  Shared L2 cache Two benchmarks  Radix (SPLASH-2) (compute intensive)  x264 (PARSEC) (memory intensive) Variables  Time interval before and after migration  Cache size and parameters 6

7. Results 7

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9. Observations Large cost variance between applications  Compute-intensive v. memory-intensive  Radix: 0.115 accesses per instruction  x264: 0.368 accesses per instruction Some sensitivity to cache parameters  Smaller cache may evict contents anyway 9

10. Future Work Refine accuracy of cost mechanism Correlate future cost with past predictors Incorporate migration cost metric into scheduling algorithm 10

11. Q&A 11