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Coscheduling in Clusters: Is it a Viable Alternative?. Gyu Sang Choi, Jin-Ha Kim, Deniz Ersoz, Andy B. Yoo, Chita R. Das Presented by: Richard Huang. Outline. Evaluation of scheduling alternatives Proposed HYBRID Coscheduling Evaluation Conclusions Discussion.

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coscheduling in clusters is it a viable alternative

Coscheduling in Clusters: Is it a Viable Alternative?

Gyu Sang Choi, Jin-Ha Kim, Deniz Ersoz, Andy B. Yoo, Chita R. Das

Presented by: Richard Huang

outline
Outline
  • Evaluation of scheduling alternatives
  • Proposed HYBRID Coscheduling
  • Evaluation
  • Conclusions
  • Discussion
evaluation of scheduling alternatives
Evaluation of Scheduling Alternatives
  • Local Scheduling
    • Processes of parallel job independently scheduled
  • Batch Scheduling
    • Most popular (Maui, PBS,etc.)
    • Avoid memory swapping, but low utilization and high completion time
  • Gang Scheduling
    • All processes of job (gang) scheduled together for simultaneous execution
    • Faster completion time, but global synchronization costs
communication driven coscheduling
Communication-Driven Coscheduling
  • Dynamic Coscheduling (DCS)
    • Uses incoming message to schedule processes for which messages are destined
  • Spin Block (SB)
    • Process waiting for message spins for fixed amount of time before blocking itself
  • Periodic Boost (PB)
    • Periodically boosts priority of process with un-consumed messages
  • Co-ordinated Coscheduling (CC)
    • Optimizes spinning time to improve performance at both sender and receiver
hybrid coscheduling
HYBRID Coscheduling
  • Idea:
    • Combines merits of both gang scheduling and communication-driven coscheduling
    • Coschedule ALL processes like gang scheduler
    • Boost process priority during communication phase
  • Issues:
    • How to differentiate between computation and communication phases?
    • How to ensure fairness during boosting?
hybrid coscheduling6
HYBRID Coscheduling
  • Boost priority whenever parallel process enter collective communication phase
  • Immediate blocking used at sender and receiver
evaluation
Evaluation
  • 16 node Linux cluster connected through 16-port Myrinet switch
  • 100 mixed applications from NAS
  • Two different job allocation
    • PACKING: contiguous nodes assigned to a job to reduce system fragmentation and increase system utilization
    • NO PACKING: parallel processes of job randomly allocated to available nodes in system
observations
Observations
  • Average performance gain for PACKING about 20% compared to NO PACKING
  • Under high load, big differences due to waiting times
  • Under light load, difference in execution time more pronounced
  • Batch scheduler has lowest execution time, followed by HYBRID
  • HYBRID has lowest completion time among all scheduling schemes
explanations
Explanations
  • HYBRID avoids unnecessary spinning
    • process immediately blocked if communication operation is not complete
  • HYBRID reduces communication delay
    • process wake up immediately upon receipt of message (since its priority boosted)
  • HYBRID avoids interrupt overheads
    • Frequent interrupts from NIC to CPU to boost process’s priority in CC, DCS, and PB
    • HYBRID boosted only at beginning of an MPI collective communication
  • HYBRID avoids global synchronization overhead like gang scheduling
    • HYBRID follows implicit coscheduling
other results
Other Results
  • Completing jobs faster can lead to energy savings by using dynamic voltage scaling or shutting down machines
  • Communication-driven coscheduling should deploy memory aware allocator to avoid expensive disk activities
conclusions
Conclusions
  • Can get significant performance improvement by using coscheduling mechanisms like HYBRID, SB, or CC
  • Block-based scheduling techniques had better results because other processes in ready state can proceed
  • HYBRID scheme is best performer and can be easily implemented on any platform with only modification in the message passing layer
  • New techniques deployed on cluster should avoid expensive memory swapping
  • Improved efficiency in scheduling algorithm can translate to better performance-energy ratio
discussion
Discussion
  • Can it be true that blocking is always better than spinning?
  • How likely is it to move away from batch scheduling in clusters and super computers?
  • Do people try to save energy by improving scheduling algorithm?