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Class Discussion

Class Discussion. Questions. What is the difference between: Remote memory access vs remote invocation? Direct vs mapped remote memory access? Interrupt vs process context remote invocation? Remote memory access vs bulk data transfer? Explicit vs implicit bulk data transfer?

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Class Discussion

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  1. Class Discussion CS533 - Concepts of Operating Systems

  2. Questions • What is the difference between: • Remote memory access vs remote invocation? • Direct vs mapped remote memory access? • Interrupt vs process context remote invocation? • Remote memory access vs bulk data transfer? • Explicit vs implicit bulk data transfer? • Why do cache coherent multiprocessors blur the distinction between remote memory access and bulk data transfer? CS533 - Concepts of Operating Systems

  3. Questions • Why not do all remote invocation in interrupt context? • Why should interrupt-level handlers for RIs not block? • What implications does this have for their ability to do synchronization? • How can you manage synchronization of data shared between interrupt and kernel process contexts for RIs? • Why should outgoing RIs be prohibited when incoming ones are disabled? CS533 - Concepts of Operating Systems

  4. Questions • How are process context RIs initiated on the receiving side? • What are the two cases we must deal with? • How are process context RIs initiated on the sending side? • How can deadlock result if the process initiating a process context RI spin-waits? • Why is blocking a better idea anyway? • Why does remote access and interrupt level RI on the same data structure require a “hybrid lock” that disables interrupts AND spins? CS533 - Concepts of Operating Systems

  5. Questions • How is the break-even point between the cost of remote access and remote invocation changing? • How is the ratio of local to remote memory access costs changing? • How is the cost of synchronization instructions changing? • How is the cost of inter-processor interrupts changing? • What are the implications of these changes for next generation (multicore) OS designs? CS533 - Concepts of Operating Systems

  6. Questions What is the difference between node locality and address locality? What leads to poor address locality in uniprocessor OSs? Node locality is important for good performance • How can you improve it? CS533 - Concepts of Operating Systems

  7. Questions • How has low memory access time influenced the design of today’s OS kernels? • Why does it encourage you to favor concurrency over locality? • Why doesn’t a simple partitioning of data into per-processor components ensure locality? CS533 - Concepts of Operating Systems

  8. Questions • Why does an object oriented structure help improve locality? • If objects represent OS abstractions such as processes and files • How much locality does this provide? • Is this enough? • How can you get more? • Does locality imply an inability to support global policies? CS533 - Concepts of Operating Systems

  9. Questions • What is a clustered object? • A collection of replicas? • Is replication for reliability? • Is replication for parallelism? • How is consistency maintained among replicas? • A collection of alternatives? • What’s the upper limit on the degree of clustering (number of replicas)? • How could you use a clustered object approach to build a distributed counter? • Why are clustered objects better suited to larger granularity object types? CS533 - Concepts of Operating Systems

  10. Questions • How should reps of a clustered object communicate with each other? • Remote access vs remote invocation? • When might you want to migrate a rep? • How do you locate the right rep to communicate with? • How much does this cost? • What if a local rep doesn’t exist yet? • How are miss-handling objects used? • Why is it worth paying the cost of a level of indirection for invocation? • Isn’t this a frequent operation that should be highly optimized? CS533 - Concepts of Operating Systems

  11. Questions • What is existence locking? • … and why does it result in lock hierarchies? • What are “temporary references”? • How can you know when there are no longer any temporary references to an object? CS533 - Concepts of Operating Systems

  12. Questions • How do locality-related issues impact memory allocation? • Why isn’t it enough to have a separate free memory pool per processor? • What’s so special about small objects? CS533 - Concepts of Operating Systems

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