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School of Computer Science & Engineering
University of New South Wales
Advanced Operating Systems
COMP9242 2002/S2
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Subsections
Issues:
- Scalability:
- How many CPUs to support?
- Application mix:
- SMP for
- time-shared multi-tasking environment,
- web server,
- highly parallel applications?
- Architecture:
- caching, memory bandwidth...
- Single scheduler for all CPUs
-
- Not really SMP.
- Not scalable.
- Global ready queue:
- CPU schedules itself from global queue.
- Course-grain locking of ready queue.
- Limited scalability.
- Per-CPU ready queues
-
- Scalable.
- Load balancing?
- Process migration?
Restrict address spaces (tasks) to a single CPU.
- +
- Most sharing is within task.
- Good cache performance (maybe?)
- +
- Unmapping pages only affects single CPU.
- Only requires invalidating local TLB entries.
- -
- No performance gain for multithreaded tasks.
- Multiple CPUs only enhance throughput.
- Not a general solution.
Always schedule all threads of a task at once on different CPUs.
- +
- Maximum concurrency for parallel applications.
- +
- Minimises intra-task communication latency.
- -
- High bus contention.
- +
- Appropriate. for parallel number-crunching
- -
- May have some CPUs idle.
==> Used mostly on supercomputers.
A thread has a processor affinity and will only run on that CPU:
- +
- Minimal contention for kernel data structures.
- +
- Minimal kernel communication overhead.
- +
- Cache friendly.
- +
- Highly scalable.
- -
- No strict global priorities.
- -
- No load balancing.
Ok for:
- non-real-time systems,
- mostly short processes,
- NUMA machines,
- with additional load balancing & process migration.
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Next: Real-time OS Issues
Up: 10-smp
Previous: Non-Uniform Memory Architecture (NUMA)
Gernot Heiser
2002-10-11
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