Clarity: Better Admission Control and Disk Scheduling for Multimedia

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Clarity Better Admission Control and Disk
Scheduling for Multimedia

• By
• Badrinath Venkatachari

Thesis Advisor Prof. Mark Claypool
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Overview

• Motivation
• Related research
• Clarity
• Implementation of Clarity
• Tests and results
• Conclusion

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Motivation

• Traditional Applications
• Text oriented applications
• Throughput and response time
• Asynchronous access
• Newer applications
• Multimedia applications (video, audio streams)
• Periodic access to disks
• Guaranteed service
• Best-effort service inadequate
• CPU much faster disk (bottleneck)

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Present Day Systems

• Best-effort service to applications
• No service differentiation
• No guarantees
• Performance degradation affects all
• Non-optimal use of resources (disk, and CPU)

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A New Framework For Content Servers

• Regulate usage of resources (admission control)
• Pessimistic (D. Anderson et al, P. Reddy et al)
• Statistical (P.Shenoy et al)
• Sampling based (P. Mohapatra et al)
• Service differentiation
• Symphony (P. Shenoy et al)
• Fellini (C. Martin et al)
• Service guarantees
• Disk scheduling
• Cello (P. Shenoy) Simulation based
• Continuous media file system (D. Anderson)
  Simulation based

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Content Servers

• Existing solutions
• Mostly pessimistic admission control
• Simulation driven
• Limited service differentiation
• Lack application oriented optimizations
• Computationally intensive
• No disk scheduler on Linux for multimedia
  applications

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Clarity Our Approach

• Admission Control
• Optimistic
• Measurement-based (adaptive)
• Cache-based (proposal)
• Disk scheduling
• Differentiated service
• Support for CBR and VBR clients
• Service guarantees
• Adaptability to system load
• Computationally efficient

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Clarity Admission Control

• Worst-case values
• Overkill
• Wastage of disk bandwidth
• Disk seek and rotational latencies average out
• Fixed (Computationally efficient)
• Reflects disk controller optimizations
• Measurement-based
• Accurate
• Better reflects system optimizations (OS and
  disk)
• Exploits special file system layout optimizations
• Sequential access of multimedia streams

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Clarity Admission Control

• Bipl Play back rate of client Ci
• B Block size (in bytes)
• bi Number of blocks to be retrieved per sec
• R Duration of a round
• Tseekavg Average seek latency
• Trotavg Average rotational latency
• Criterion for admission in the presence of n
  clients

? bi (Tseekavg Trotavg) lt ?
R, where, ? is the percentage of bandwidth
reserved for multimedia clients
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Clarity Disk Scheduling

• Service Classes
• Loss tolerant multimedia clients
• Disk requests can be dropped, but the ones that
  are delivered are on time
• Typical soft-real time applications
• Delay tolerant multimedia clients
• Disks cannot be dropped, but can be delayed
• Streams with very important information where all
  video and audio needs to be played back

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Clarity Disk Scheduling

• Service Classes
• Non-essential non-multimedia clients
• Traditional applications like ftp, and http
• Essential non-multimedia clients
• Systems requests to disk on page faults etc.
• Special category that cannot be blocked under any
  circumstances
• No special bandwidth reservation for this class

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Clarity Disk Scheduling

• Inter-service class protection
• Protect clients from one class against abuse from
  clients belonging to other classes
• Delays forwarding request to the disk queue by
  putting on a WAIT_QUEUE
• Intra-service class protection
• Protect clients within a class from one another
• Delays requests once clients admitted rate has
  been met using a WAIT_QUEUE.
• Clarity monitors for excess bandwidth that can be
  shared among clients needing additional data

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Clarity Disk Scheduling

• Adaptability to system load
• Pro-active approach to bandwidth re-assignment
• Bandwidth re-assigned from class not needing it
  to one that needs it
• Bandwidth adjusted if at a later time disk
  request from a under-utilized class increases
• Increases disk utilization

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Clarity Implementation

• Processor Pentium
• Speed 133 MHz (66 Bogomips)
• RAM - 128 MB
• Disk Space 4 GB
• Kernel Linux 2.0.36

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Tests and Results

• Admission Control
• Number of clients admitted
• Deadlines missed
• Bandwidth partitioning

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Tests and Results

• Disk Scheduling
• Raw throughput performance
• Inter-service class protection
• Intra-service class protection
• Bandwidth re-allocation
• Overloaded rounds

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Tests and Results (Admission Control)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Tests and Results (Disk Scheduling)
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Conclusions

• Admission Control
• Optimistic and Measurement better than
  pessimistic
• Adaptive admission control increases disk
  utilization

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Conclusions

• Disk Scheduler
• Raw throughput and response time comparable to
  vanilla Linux in absence of multimedia clients
• Inter-service class protection
• Guarantees bandwidth to multimedia clients
• Prevents degradation in throughput and response
  time
• Intelligent bandwidth re-allocation
• Helps media scaling under over-loaded conditions

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Future Directions

• Cache-based admission controller
• File systems for multimedia streams
• Disk layout of files
• Integrated framework of process and disk scheduler