CSL seminars - Summer 2012
Location and time:
BA5256, Friday 12-1pm
Trickle: Rate Limiting YouTube Video Streaming
YouTube traffic is bursty. These bursts trigger packet
losses and stress router queues, causing TCP's
congestion-control algorithm to kick in. In this paper,
we introduce Trickle, a server-side mechanism that
uses TCP to rate limit YouTube video streaming. Trickle
paces the video stream by placing an upper bound on
TCP's congestion window as a function of the streaming
rate and the round-trip time. We evaluated Trickle on
YouTube production data centers in Europe and India
and analyzed its impact on losses, bandwidth, RTT, and
video buffer under-run events. The results show that
Trickle reduces the average TCP loss rate by up to 43%
and the average RTT by up to 28% while maintaining
the streaming rate requested by the application.
Monia is PhD candidate in Systems and Networking group
at University of Toronto. Her research interests are in
the general area of computer networking, including data
center networking, transport protocols, switch and router
architecture, resource management, network measurement,
and online social networks. In the past she worked on
sizing buffers in Internet routers.
Practical Scrubbing: Getting to the bad sector at the right time
Latent sector errors (LSEs) are a common hard disk failure mode, where disk sectors
become inaccessible while the rest of the disk remains unaffected. To protect against LSEs,
commercial storage systems use scrubbers: background processes verifying disk data. The efficiency
of different scrubbing algorithms in detecting LSEs has been studied in depth; however, no attempts
have been made to evaluate or mitigate the impact of scrubbing on application performance.
In this talk, we provide the first known evaluation of the performance impact of different scrubbing
policies in implementation, including guidelines on implementing a scrubber. To lessen this impact,
we present an approach giving conclusive answers to the questions: *when* should scrubbing requests
be issued, and at *what size*, to minimize impact and maximize scrubbing throughput for a given
workload. Our approach achieves six times more throughput, and up to three orders of magnitude
less slowdown than the default Linux I/O scheduler.
George is a Ph.D. student in the Computer Systems and Networks group at the
University of Toronto. His current research revolves around storage reliability and component idleness
characterization, detection and utilization. He completed his B.Sc. at the University of Ioannina in
Greece, with a B.Sc. thesis studying namespace management techniques for federated filesystems.
Towards the contention aware scheduling in HPC cluster environment
Contention for shared resources in High-Performance Computing (HPC) clusters
occurs when jobs are concurrently executing on the same multicore node
(there is a contention for shared caches, memory buses, memory controllers
and memory domains). The shared resource contention incurs severe degradation
to workload performance and stability and hence must be addressed.
The state-of-the-art HPC clusters, however, are not contention-aware.
The goal of this work is the design, implementation and evaluation of a
virtualized HPC cluster framework that is contention aware.
Sergey Blagodurov is a Ph.D. Candidate in School of Computing Science at
Simon Fraser University, Vancouver, Canada. His research focuses on resource
contention-aware scheduling in High-Performance Computing (HPC) clusters of
multicore machines and exploring new techniques to deliver better performance
on non-uniform memory access (NUMA) multicore systems under Linux. He is also
a Research Associate at HP Labs, where he studies the design and operation of
net-zero energy data centers.
Automatic Device Driver Synthesis
Faulty device drivers are the leading source of reliability problems
in modern operating systems. Automatic device driver synthesis is a
radical approach to creating drivers faster and with fewer defects.
In this talk I will give an overview of the game-based approach to
device driver synthesis, where a correct driver implementation is
obtained as a winning strategy in a game played by the driver against
the device and its physical environment. I will list the main challenges
involved in synthesising drivers for complex real-world devices and
will present our driver synthesis tool called Termite.
Leonid Ryzhyk completed his Ph.D. in 2010 under Gernot Heiser
at the University of New South Wales and NICTA. His PhD and
subsequent work (mostly in collaboration with Intel Labs)
has been on making device drivers more reliable. Some of his
work was published in HotOS, SOSP, ASPLOS, and EuroSys.