Lecture 4 Flashcards

1
Q

What are the Cloud Resource Management Policies?

A
  • Admission Controlprevent the system from accepting workload in violation of the high-level policies.
  • Capacity allocationallocate resources for individual activities of a service.
  • Load balancingdistribute the workload evenly among the servers.
  • Energy optimisation – minimise energy consumption
  • Quality of service (QoS) guarantees – ability to satisfy timing or other conditions specified by Service Level Agreement
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2
Q

What is scheduling?

A
  • Responsible for resource sharing + time to allocate: CPU Cycles, memory, secondary storage space, I/O + network bandwidth between users and tasks
  • Scheduler: A program that implements a particular scheduling algorithm

Affects 3 criterias:

  • Functionality
  • Performance
  • Cost
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3
Q

What are the policies and mechanism for resource allocation

A
  • *Policies** – principles for guiding decisions
  • *Mechanisms** – Implement policies
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4
Q

What are the common Scheduling algorithms?

A
  • Round-robin
  • First-Come-First-Serve
  • Shortest-Job-First
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5
Q

What are the Scheduling Algorithm Policies?

A
  • Best-effort policies – Impose requirements regarding enter the amount of resource allocation to an application when scheduled.
  • Soft-requirements policies – require statically guaranteed amounts + timing constraints
  • Hard-requirements policies – demand strict timing and precise amounts of resources
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6
Q

What are the Cloud Scheduling Subject to Deadlines?

A
  • Hard deadlines – Task not completed by the deadlines, other tasks depend on it will be affected with penalties and expressed as milliseconds
  • Soft deadlines – More of a guidelines with no penalties, can be missed by fractions of the units
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7
Q

What are the considerations required in Resource Management in Virtualised Servers?

A

Considerations

  • Many different workloads
  • Finite numbers of workloads can be hosted on each server
  • Timing varying workload requirements
  • Performance and resource isolation among the workloads
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8
Q

What is a Proportional Share (PS) and it’s evaluation?

A
  • allocates CPU in proportion to the number of shares_,_ VM’s are assigned to

Evaluation –

  • Fairness – time interval over the scheduler provides fair CPU allocation
  • Allocation error – difference between the allocation and real demanded allocation
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9
Q

Fair-share Vs Proportional Scheduling

A

Fair-share schedulers attempt to provide time-averaged form of proportional shared based on the usage over time periods

Work-conserving (WC-mode)

  • CPU shares are merely guarantees: there is work to be done; all clients have used shares the CPU will be used

Non work-conserving (NWC mode)

  • CPU shares are caps. Clients will get their share of CPU
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10
Q

What is the difference between Non-Preemptive and Preemptive schedulers?

A

Non-Preemptive schedulers

  • Schedulers allow running clients to finish their CPU slice. Schedulers make decisions once the running client gives up the CPU.

Preemptive schedulers

  • Running clients can be preemptive for other clients to run. Schedulers rerun their scheduling decisions when a new client arrives
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11
Q

What is Workload Management?

A
  • Workload assigns (CPU, memory, I/O) resources to applications.
  • Applications provide service levels on their desired performance + workload managers assign resources to comply to these levels.
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12
Q

What are the Workload management approaches?

A

Static: Resources are estimated once + assigned statistically applications

Dynamic: Dynamically allocate resources to match applications workload resource demands

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13
Q

What are the Xen CPU schedulers?

A
  • Borrowed Virtual Time (BVT)
  • Simple Earliest Deadline First (SEDF)
  • Credit Scheduler
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14
Q

What is Borrowed Virtual Time (BVT)?

A
  • a fair-share scheduler based on the concept of virtual time, dispatching thread with runnable VM with the lowest virtual time first
  • Allows latency-sensitive applications borrows virtual time to gain scheduling priority + applications borrow virtual time from its future allocation

Features:

  • Preemptive, WC- code only
  • Optimally-fair;
  • Low overhead implementation on multiprocessors
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15
Q

What is Simplest Earliest Deadline First (SEDF)?

A

Runnable domain with the earliest deadline is picked + scheduled

Features:

  • Preemptive, WC, NWC modes
  • Fairness depends on the value of a period
  • Implements per CPU queue, lacks global load balancing on multiprocessors
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16
Q

What is Credit Scheduler?

A
  • Xen’s latest PS scheduler featuring automatic load balancing of virtual CPUs across physical CPUs on SMP host
  • Before a physical CPU goes idle it will consider runnable vCPUs to run

Goal: Guarantees no CPU idles when there is runnable work in the system

  • VM assigns weight + cap
  • If cap is 0, the VM receives extra time (WC-mode)
  • If cap is non-0, the max time it can receive (NWC)
17
Q

What are the Experimental comparison of the three schedulers benchmarks?

A

3 benchmarks:

  • Webserver application to measure web server throughput
  • Iperf to measure the maximum achievable network throughput
  • Disk read to measure disk and read throughput