Research
Elizabeth Varki
Department of Computer Science
University of New Hampshire
Kingsbury Hall
Durham, NH 03824
Phone: (603) 862-2319
Email: varki@cs.unh.edu
www: www.cs.unh.edu/~varki
My area of expertise is performance evaluation. I evaluate the performance of
computer and communication systems, storage devices, and software systems.
I am a modeler: real-world is complex and it is difficult to understand what
features of the real-world drives performance. For example,
when you click a link on your web browser, what determines the speed with which
the page is downloaded on your computer - the speed of your computer, or
the network bandwidth, or the speed of
the web server, or some other factor? This leads to further questions:
what determines the speed of your computer - the CPU speed or the
cache size or the memory bus speed - leading to futher evaluation at lower levels.
There are many, many parameters in a real system, which makes it difficult to see the
forest for the trees. I determine what
parameters are essential to determining the performance
of the real-world system under consideration. I then develop a mathematical model
that incoporates only those parameters that drive the performance.
Thus, my model is an abstraction of the real system that incoporporates the
essential parameters that drive performance. This model can then be used
to understance the behavior of the real system.
I develop performance models which compute mean performance measures such
as response time and throughput. These are articulated by queueing models.
When computing performance of distributed systems - computers around the globe
connected by the Internet - I use graph models.
Once I develop the model, I use existing algorithms, to compute performance
measures from the model.
If algorithms/tools to compute mean performance measures from the model
do not exist, then I develop (or try to develop) the algorithm.
I develop new technology if existing technology is not keeping pace with
improvements in hardware and software. For example, my student and I have
developed RAIDX for arrays of dissimilar disks since RAID was developed for
arrays of similar disks.
Listed below are my papers, classified by topic, starting from my most recent
research interests. It is ironic that my best papers on most topics haven't been
published.
RAIDX: RAID for heterogenous array of disks
We propose a new organization for organizing an array of disks of different types,
sizes, and speeds. RAIDX does not stripe data across disks, it bundles chunks of data
across disks.
GPSclock: A performance model to track time and flow capacity of end networks
A graph model that models time at end networks. The time determines the available
bandwidth capacity, so this graph models flow capacity at end networks. This model
underlies maximal flow problems between end networks.
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E. Varki.
Crowd Supported Maximum Flow from Sender to Receiver, 2016.
-
E. Varki.
Users at End Networks Collaborating for Maximum Flow, 2015.
-
E. Varki.
Modeling bulk transmission with a star graph, 2015.
-
E. Varki.
Modeling Maximum-Flow over the Internet with a Star Graph, 2015.
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E. Varki.
Modeling the internet for maximal flow when capacity varies with local time, 2014.
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E. Varki, Q. Liu, A. Villa.
Beyond flow networks: Internet flow routing with clock nets, 2014.
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E. Varki.
Modeling time-synchronized dynamic flow in internet, 2014.
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E. Varki, Q. Liu, A. Villa.
Beyond flow networks: global flow routing with clock nets, 2013.
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E. Varki, Q. Liu, A. Villa.
short version.
Longer version.
Flow Network Model of Bulk Transmission, 2013.
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E. Varki, Q. Liu, A. Villa.
A new model to evaluate bulk transmission over the internet, 2013.
- A. Villa, E. Varki
Performance evaluation of big data transmission models.
CMG (Computer Measurement Group), December 2013.
- A. Villa, E. Varki
Tortoise vs. hare: a case for slow and steady
retrieval of large files.
2nd International Conference on Advanced
Computing and Communications (ACC 2012), June 2012.
- A. Villa, E. Varki
Characterization of a campus Internet workload.
27th International Conference on Computers and their
Applications (CATA), March 2012.
-
A. Villa, E. Varki
The feasibility of moving terabyte files between
campus and cloud. 23rd IASTED International Conference on Parallel and
Distributed Computing and Systems (PDCS). December 2011.
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A. Villa, E. Varki
It takes know-how to retrieve large files over public networks.
ISCA First International Conference on Advanced Computing and Communications, ACC 2010, September 2010.
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A. Villa, E. Varki
Co-allocation in data grids: A global, multi-user perspective.
Advances in Grid and Pervasive Computing - Third International Conference, GPC 2008, Lecture Notes in Computer Science, pages 152–165, 2008.
-
A. Villa, E. Varki
Replica traffic manager for data grids.
In 20th ISCA International Conference on Parallel and Distributed Computing Systems, September 2007
Prefetch cache replacement technique
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E. Varki, A. Hubbe, A. Merchant.
Significance of Replacement Queue in Sequential Prefetching.
Computer Measurement Group (CMG) International Conference, December 2012.
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E. Varki, A. Hubbe, A. Merchant.
Improve prefetch performance by splitting the cache replacement queue
Springer Lecture Notes in Computer Science, March, 2013. Also,
IEEE International Conference on Advanced Infocomm Technology (ICAIT'12),
July 2012.
-
E. Varki, A. Hubbe, A. Merchant.
Improve prefetch performance by splitting the cache replacement queue
Technical paper, 2012.
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E. Varki, A. Hubbe, A. Merchant.
The Split replacement policy for caches with prefetch blocks
Technical paper, 2011.
-
E. Varki.
Removing Belady's Anomaly from Caches with Prefetch Data, 2011.
Prefetch cache
Arrival queues
Fibre channel
RAID
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E. Varki, A. Merchant, J. Xu, X. Qiu
Issues and challenges in the performance analysis of real disk arrays,
IEEE Transactions on Parallel and Distributed Systems,
July 2004.
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E. Varki, A. Merchant, J. Xu, X. Qiu
An integrated performance model of disk arrays,
[PDF],
IEEE/ACM MASCOTS 2003.
-
E. Varki, A. Merchant, J. Xu, X. Qiu
Analytical performance model of disk arrays,
[PDF],
Technical report.
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A. Gandhi, E. Varki, S. Bhatia,
Reader-Writer Locks for Network Attached Storage and
Storage Area Network,
[PDF],
ISCA 17th International Conference on Computers and their Applications},
San Francisco, CA, April 2002.
-
E. Varki, S.X. Wang,
A performance model of disk array storage systems,
[PDF],
The Computer Measurement Group's 2000 International Conference,
Orlando, Florida, December 2000.
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C. Childers, E. Varki,
The performance of non--redundant striping in a SSA disk array,
[PDF version],
Proceedings of the 12th International Conference on
Parallel and Distributed Computing Systems,
August 1999, pp. 63 -- 68.
Fork-Join queues
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E. Varki, L.W. Dowdy, C. Zhang,
Quick performance bounding techniques for computer and storage systems with
parallel resources,
[PDF version], 2002.
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E. Varki, A. Merchant, H. Chen,
The M/M/1 Fork-Join Queue with Variable Sub-Tasks,, 2002.
-
E. Varki,
Response time analysis of parallel computer and storage
systems,,
[PDF version],
IEEE Transactions on Parallel and Distributed Systems, Vol 12. No. 12,
November 2001.
-
E. Varki,
Mean value technique for closed fork-join networks,
[PDF version],
Proceedings of ACM SIGMETRICS Conference on Measurement and
Modeling of Computer Systems,
Atlanta, GA, May 1999, pp. 103 -- 112.
Also, Performance Evaluation Review, 27, 1.
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E. Varki, L.W. Dowdy,
Analysis of balanced fork-join systems,
[PDF version],
Proceedings of ACM SIGMETRICS Conference on the Measurement
and Modeling of Computer Systems, Philadelphia, PA, May 1996.
Also, Performance Evaluation Review, 22, 1.
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E. Varki, L.W. Dowdy,
Exact response time analysis of two server
systems,
[PDF version],
Proceedings of the 4th International Workshop on
Modeling, Analysis, and Simulation of Computer and
Telecommunication Systems, San Jose, California, February 1996,
pp. 287 --295.
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