69,414 research outputs found
WMTrace : a lightweight memory allocation tracker and analysis framework
The diverging gap between processor and memory performance has been a well discussed aspect of computer architecture literature for some years. The use of multi-core processor designs has, however, brought new problems to the design of memory architectures - increased core density without matched improvement in memory capacity is reduc- ing the available memory per parallel process. Multiple cores accessing memory simultaneously degrades performance as a result of resource con- tention for memory channels and physical DIMMs. These issues combine to ensure that memory remains an on-going challenge in the design of parallel algorithms which scale. In this paper we present WMTrace, a lightweight tool to trace and analyse memory allocation events in parallel applications. This tool is able to dynamically link to pre-existing application binaries requiring no source code modification or recompilation. A post-execution analysis stage enables in-depth analysis of traces to be performed allowing memory allocations to be analysed by time, size or function. The second half of this paper features a case study in which we apply WMTrace to five parallel scientific applications and benchmarks, demonstrating its effectiveness at recording high-water mark memory consumption as well as memory use per-function over time. An in-depth analysis is provided for an unstructured mesh benchmark which reveals significant memory allocation imbalance across its participating processes
Securing a Quantum Key Distribution Network Using Secret Sharing
We present a simple new technique to secure quantum key distribution relay
networks using secret sharing. Previous techniques have relied on creating
distinct physical paths in order to create the shares. We show, however, how
this can be achieved on a single physical path by creating distinct logical
channels. The technique utilizes a random 'drop-out' scheme to ensure that an
attacker must compromise all of the relays on the channel in order to access
the key
Playing Games with Quantum Mechanics
We present a perspective on quantum games that focuses on the physical
aspects of the quantities that are used to implement a game. If a game is to be
played, it has to be played with objects and actions that have some physical
existence. We call such games playable. By focusing on the notion of
playability for games we can more clearly see the distinction between classical
and quantum games and tackle the thorny issue of what it means to quantize a
game. The approach we take can more properly be thought of as gaming the
quantum rather than quantizing a game and we find that in this perspective we
can think of a complete quantum game, for a given set of preferences, as
representing a single family of quantum games with many different playable
versions. The versions of Quantum Prisoners Dilemma presented in the literature
can therefore be thought of specific instances of the single family of Quantum
Prisoner's Dilemma with respect to a particular measurement. The conditions for
equilibrium are given for playable quantum games both in terms of expected
outcomes and a geometric approach. We discuss how any quantum game can be
simulated with a classical game played with classical coins as far as the
strategy selections and expected outcomes are concerned.Comment: 3 Figure
Extending the Reach of QKD Using Relays
One of the obstacles to deployment of QKD solutions has been the distance
limitation. Solutions using relays have been proposed but these rely on
link-by-link key establishment. We present a new technique to extend the
distance of a quantum key distribution channel using an active relay. Each
relay acts as an intercept/resend device and allows the establishment of an
end-to-end key. It has been argued that such relays cannot be used to extend
the distance, but we show that with a suitable adaptation of the protocol the
effective key distribution distance can be increased
Parallelising wavefront applications on general-purpose GPU devices
Pipelined wavefront applications form a large portion of the high performance scientific computing workloads at supercomputing centres. This paper investigates the viability of graphics processing units (GPUs) for the acceleration of these codes, using NVIDIA's Compute Unified Device Architecture (CUDA). We identify the optimisations suitable for this new architecture and quantify the characteristics of those wavefront codes that are likely to experience speedups
Composite fermion model for entanglement spectrum of fractional quantum Hall states
We show that the entanglement spectrum associated with a certain class of
strongly correlated many-body states --- the wave functions proposed by
Laughlin and Jain to describe the fractional quantum Hall effect --- can be
very well described in terms of a simple model of non-interacting (or weakly
interacting) composite fermions.Comment: 6 pages, 2 figure
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