CS655-Alsaraan-MapReduce

CS655-Alsaraan-MapReduce

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Unformatted text preview: h may not hold. Figure 2 from [6] 27 28 Incorrect Es�mated Times v  2 Situa�ons: Second Approach v  A task’s progress rate slows down: caused the problem. v  A task’s progress rate speeds up: no problem here. v  This problem is not frequent in typical MR jobs: v  Reduce tasks are slow in their first phase then speed up. v  A possible solu�on for the less typical MR jobs: v  Account for each phase independently (per-­‐phase progress rate) 29 30 5 9/17/13 Three Approaches to Improve the Performance MR Job v  MapReduce Group Scheduler (MRG), by Kang et al. [2]. MR Job Tasks Second Approach Tasks v  A VM scheduler for scheduling the VMs on the physical machines (proposed as an extension to Xen). LATE [6]: Specula�ve Task Scheduler v  Inefficiencies of Xen: v  MR tasks are I/O-­‐bound à increase context switch P2P-­‐MR [3]: Architecture Change overhead Nodes v  Boos�ng a VM frequently can cause scheduling delay of other VMs on the same machine. Virtualized Machines v  Observa�on: For a MR job, its VMs have similar behavior. MRG [2]: VM Scheduler Physical Machines 31 MR Job Characteris�cs 32 Xen’s Credit Scheduler v  Most MR jobs are data-­‐intensive à I/O-­‐bound tasks. v  VMs are assigned credits used to schedule them on the CPU. v  Frequent I/O requests from each VM v  à Addi�onal overhead on the VMM. v  Priority order: boost > under > over > idle. v  The VM will be put in the wait queue a�er an I/O request, v  The run queue is sorted by the priori�es. and then back to the top of the run queue when the event is delivered by the driver domain. v  VMs loose some credit when de-­‐scheduled a�er allocated �me slice. v  à limits responsiveness to the other VMs. v  dom0 (special driver domain -­‐ the layer between the v  For a MR job, its VMs have similar behavior. VMs and the PM) handles all I/O processing. 33 Xen’s Credit Scheduler 34 Example v  4 domains are running on the same PM: v  If a VM request I/O, the request is passed to dom0 and v  dom0: driver domain the VM goes to the wait queue. v  dom1 and dom2 belong to a MR job, while dom3 belongs v  When dom0 is scheduled on CPU, it handles any pending to another. I/O requests. v  Upon comple�on of an I/O request, the VM is boosted in the run queue to handle the I/O. v  Scheduling dom0 too o�en incurs higher context switch overhead with fewer I/O handling per scheduling. Figure 3 from [2] v  The driver domain dom0 is scheduled a�er every de-­‐ scheduling of the VMs. 35 36 6 9/17/13 In addi�on to unfairness, they can be considered as stragglers. Example MRG Scheduler v  Idea: use the knowledge about the groups for MR jobs. v  To reduce context switch overhead: v  Instead of sor�ng the CPU run-­‐queue only using FIFO within each priority, it groups by MR job too. v  Defers dom0 to a�er a MR job group. Figure 4 from [2] If dom0 scheduling is deferred un...
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This note was uploaded on 02/11/2014 for the course CS 655 taught by Professor Shrideeppallickara during the Fall '13 term at Colorado State.

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