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Parallel OS

Parallel OS . Goals and Constraints. I, too can have a cartoon. OS. application. application. OS. hardware. implements virtual machine seen by application software higher level of abstraction than HW can be runtime! provides protection & error recovery performs resource management

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Parallel OS

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  1. Parallel OS Goals and Constraints

  2. I, too can have a cartoon

  3. OS application application OS hardware • implements virtual machine seen by application software • higher level of abstraction than HW • can be runtime! • provides protection & error recovery • performs resource management • because system goal function application goal function • resources are allocated “on demand” • works when each app uses small fraction of total resources • OS predicts future application needs, based on past behavior • OS is autonomous

  4. Key Questions • Does “parallel OS” define right virtual machine? • Does is apply right resource management policies? • Does it provide required protection & recovery?

  5. Cluster OS parallel application global OS global OS node OS node OS node OS node hw node hw node hw switch • Node OS is full-fledged Unix system • Global OS is set of cluster services built atop Unix networking APIs

  6. Problems • Very limited set of global services, with low performance, since atop networking APIs • Local resource management decisions are often wrong, since based on local information and on irrelevant time sharing model • No distinction between internal and external allocation • Resource management is too fine grain • E.g.: mem management, global malloc (same address everywhere), dynamic gang scheduling (comm variance) • IO: • node asynchronous IO • global blocking IO, for long delay events (msecs) • global swap, for very long delay events (secs)

  7. Desired Structure parallel app parallel app runtime runtime global resource manager virtual parallel machine virtual parallel machine • Each parallel application is provided with a “dedicated virtual parallel machine” • E.g. space partition, for a long time block • changes in VPM resources are rare and are negotiated • Hw provides protection across VPMs • resource management inside VPM done by runtime • thread scheduler, memory manager, IO…

  8. Implementation parallel application global runtime global runtime node runtime node runtime node runtime global OS global OS OS proxy OS proxy OS proxy node hw node hw node hw switch • OS proxy is local representative of global OS • attaches/detaches resources to/from VPM • handles exceptions • does not implement local policies • does not manage VPM resources

  9. Global runtime abstractions • Collective service invocations • collective IO, collective malloc,… • Scalable, associative individual invocations • call logically made to global server • actually serviced by local proxy or “regional” proxy • associative service: throughput scales with number of servers • e.g. global queue • also gains locality

  10. Where does OS run? • Local proxy must run on local node • may mostly use semi-dedicated resources? (separate CPU in large SMP node) • Global OS logic may run at dedicated server nodes or be distributed all across, or both • answer not obvious with large SMP nodes and modern interconnects

  11. Shared Memory OS – is it different? • Many differences of detail – same global structure • need local proxies for performance and fault isolation • need recoverable/transactional communication protocol between proxies (message passing?) • may have more logical/flexible definition of “node” • VPM has global shared memory, protected by hw from other VPMs, and managed by runtime

  12. Why “ideal OS” will not come from commercial system vendors? • Weaker requirement for strong coupling across nodes in most commercial environments • Desire to avoid high-end unique technology • Strong reluctance to revisit established boundaries (OS/runtime/compiler/…) • which are also organizational boundaries… • Possible commodization of OS • all action is in the middleware • Cost of testing, even for minute changes • Risk avoidance and lack of expertise

  13. Why “ideal OS” may come from commercial vendors • Needs of large subsystems • DB, web servers… • Needs of new hw architectures • Security problems in large, monolithic kernels

  14. Possible path • Revisit “Sandia design”, in light of larger SMP nodes • heavy server node with general purpose OS • light compute node with simple exec, managing single user process • derived from real-time OS? from Linux? • Develop global OS functions incrementally • Ensure that future architectures provide right hw protection mechanisms to enable user runtime VPM management • take advantage of hw support of hypervisor?

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