CMT OS scheduling summary Yipkei Kwok 03/18/2008

Homogeneous Scheduling Where are we now? –Fairness/performance isolation Cache-fair thread scheduling for multicore processors Performance of multithreaded chip multiprocessors and implications for operating system design –Achievement 24% reduction in performance variability

Homogeneous Scheduling Where are we now? –Performance optimization A Non-Work-Conserving Operating System Scheduler For SMT Processors Symbiotic Job Scheduling for a Simultaneous Multithreading Architecture –Achievement Performance improvement for up to 45%

Homogeneous Scheduling Un-investigated problem –Most techniques are developed for small scale machines (e.g. 18 threads for SPEC2000 and 8 hardware contexts) –Work well on large scale CMT machines? –Some techniques requires virtually no overhead w./ hardware support. – fine –Some co-scheduling techniques examine nCr combinations (n=no. of workloads, r=degree of parallelism) –New Moore’s law (joke): no. of cores doubles every 18 months.

Homogeneous Scheduling Un-solved problem –Desktop workload optimization Why is it hard? –Short running time –Unpredictable behavior –Limited level of parallelism –Light Desktop workloads becoming heavier and long-running App-hinted OS scheduling –Thread Scheduling for Multi-Core Platforms. Mohan Rajagopalan Brian T. Lewis Todd A. Anderson. HotOS '07. App developers forces to explore parallelism.

Heterogeneous Scheduling Where are we now? –Couple papers –Limited to cores w./ same ISA but different speeds –Can you find one in the market?

Heterogeneous Scheduling Scheduling objectives (same ISA) –Performance optimization –Fair CPU sharing –Balanced core assignment Scheduling objectives (different ISA) –Unidentified –Balanced core assignment not applicable –How do you avoid performance jitters?

Heterogeneous Scheduling More problems –Preferred core dilemma –Follow/not follow when the preferred core has a long queue? Follow -> long response time Not follow -> sub-optimal performance –How does the decision affect the overall performance?