implementation and evaluation of a multimedia file system t.n.niranjan tzi-cker chiueh gerhard a....
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Implementation and Evaluation of a Multimedia File System
T.N.Niranjan Tzi-cker Chiueh Gerhard A. Schloss
Department of Computer Science State University of New York at Stony Brook 1997 IEEE
Presented by Sharon Shen
OVERVIEW
IntroductionRelated WorkMMFS DesignPerformance EvaluationConclusions and future work
INTRODUCTION
Multimedia unique demands in file system MMFS extends UFS Supports a two dimensional file structure
– Single medium editing– Multiple-media playback environments
A fully functional file system based on the VFS
INTRODUCTION
Classification of multimedia applications– Playback oriented
Concerned with real-time constraints and synchronized retrieval
– Development orientedRequire system support to manipulate
compositions
INTRODUCTION
MMFS offers a set of functionalities for multimedia support– Synchronized multi-stream retrieval– Editing support– Caching and prefetching optimizations– Real-time disk scheduling
RELATED WORK
UCSD multimedia serverCMFSMitra & SBVS IBM Tiger SharkYARTOS
RELATED WORK
Tactus toolkit & Acme I/O Server Audition audio system MMFS could not provide real-time
guarantees to multimedia playback– Vagaries of the FreeBSD process scheduler– Lack of admission control– Re-implementation on Unix OS augmented with
real-time support make this feature feasible
MMFS DESIGN
Extends the UNIX file structure– A single-medium strand abstraction– An MM file construct: tie multiple strands– An MM file is associated with unique
mnodeMnode contains the metadata of the MM fileMutimedia-specific metadata of each strand(recording rate,logical block size, the size of
the application data unit)
MMFS DESIGN
Reduction of the “impedance mismatch” between the multimedia applications and the file system– Used for low-level optimization– MMFS API
Add an extra argument mminfo Add/Remove strands from an MM fileInsert/Delete data from strands
MMFS DESIGN Prefetching
Unix file system– Sequential reads are common– Each open file is associated with a read-
ahead length(v_ralen) in its vnode– Not sequential readprefetching is avoid
and exponential back-off of v_ralen is initiated
MMFS DESIGN Prefetching
Playback of a video in reverse– UFS identify non-sequential readreduce
the degree of prefetching– MMFS allows the application to advise
the file system reverse the directionSetting mminfo->direction to REVERSEPassing mminfo as an argument to mmread
MMFS DESIGN Prefetching
Playback of a video in fast-forward– UFS Prefetching ( issue read-aheads for
unnecessary blocks)
MMFS DESIGN Prefetching
Playback of a video in fast-forward– MMFS perform intelligent prefetching
Applications communicate MMFSSetting the fields in mminfo (retrieval
rate,direction,whether frames skip)Degree of prefetching is maintained at a high
levelNote: It does not work for compressed data streams
MMFS DESIGN
Prioritized real-time disk scheduling
UFS using SCAN– Order the request by the position of the
requested physical block on the disk surface
– nonRT operations queued with RT multimedia operations
MMFS DESIGN
Prioritized real-time disk scheduling
MMFS using priority– Higher priority = RT request, lower priority =
nonRT request– Non-preemptive Scheduling – Assign a deadline with each mmread request– Use Earliest Deadline First scheduling for RT
use SCAN for nonRT request– Starvation possible for nonRT
MMFS DESIGN
Support for synchronization
Quality of synchronization measured by the amount of skew
MMFS considers each strand as a temporally continuous stream of data
Specify mmbind, synchronized retrieval the given strands
MMFS constructs a round-robin retrieval schedule for these strands
An mmunbind call issued when synchronization is no longer required
MMFS DESIGN
Support for Editing
UFS use write, truncate system calls for small size file
Multimedia editing large uncompressed files
MMFS provide mminsert and mmdelete
MMFS PERFORMANCE EVALUATION Evaluation Environment
Multimedia data residing in local IDE disk of Pentium-90
Compare MMFS with UFS of FreeBSD 2.0.5
MMFS PERFORMANCE EVALUATION Impact of prefetching optimization
Parameters of experiment
MMFS PERFORMANCE EVALUATION Impact of prefetching optimization
Response Time: time taken between the issuance of read request and the reception of the request data
Delayed: If the response time is more than 130% of the frame duration
Performance metric: fraction of delayed frames
MMFS PERFORMANCE EVALUATION Impact of prefetching optimization
Reverse playback
MMFS PERFORMANCE EVALUATION Impact of prefetching optimization
Fast forward playback
MMFS PERFORMANCE EVALUATION Impact of prefetching optimization
Fast reverse playback
MMFS PERFORMANCE EVALUATION Impact of prioritized RT disk scheduling
Effect of nonRT load
MMFS PERFORMANCE EVALUATION Impact of prioritized RT disk scheduling
Effect of RT load
MMFS PERFORMANCE EVALUATION Impact of synchronization support
Multi-Strand Playback
MMFS PERFORMANCE EVALUATION Impact of synchronization support
CONCLUSIONS & FUTURE WORK
UFS assumptions and design decision are not appropriate for multimedia
MMFS prefetching optimization allow applications to playback streams at higher access rate and different directions
MMFS disk scheduler maintains the performance of the multimedia application when RT and nonRT application are simultaneously active
CONCLUSIONS & FUTURE WORK
MMFS editing primitives offer an excellent response to development applications
MMFS bridges the gap between generic file systems and special-purpose servers
MMFS provides real-time process scheduling to meet QoS requirements
CONCLUSIONS & FUTURE WORK
The idea embedded in MMFS are widely applicable to any general-purpose file system
Many enhancements to the current implementation are possible
The impact of variable-rate compression on MMFS optimizations have to be studied
The feasibility of extending MMFS to a distributed environment deserves investigation
REFERENCES
Niranjan, T. N. File System Support for multimedia applications. PhD thesis, SUNY at Stony Brook, December 1996. At http://www.cs.sunysb.edu/~niranjan/thesis.ps.gz
Niranjan, T. N. and Schloss. F. State-based buffer-cache design for a multimedia file system. In Proc. Of the Sixth Int. Workshop in Network and Operating System Support for Digital Audio and Video(NOSSDAV), April 1996
Q & A
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