4,303 research outputs found
GraphBLAST: A High-Performance Linear Algebra-based Graph Framework on the GPU
High-performance implementations of graph algorithms are challenging to
implement on new parallel hardware such as GPUs because of three challenges:
(1) the difficulty of coming up with graph building blocks, (2) load imbalance
on parallel hardware, and (3) graph problems having low arithmetic intensity.
To address some of these challenges, GraphBLAS is an innovative, on-going
effort by the graph analytics community to propose building blocks based on
sparse linear algebra, which will allow graph algorithms to be expressed in a
performant, succinct, composable and portable manner. In this paper, we examine
the performance challenges of a linear-algebra-based approach to building graph
frameworks and describe new design principles for overcoming these bottlenecks.
Among the new design principles is exploiting input sparsity, which allows
users to write graph algorithms without specifying push and pull direction.
Exploiting output sparsity allows users to tell the backend which values of the
output in a single vectorized computation they do not want computed.
Load-balancing is an important feature for balancing work amongst parallel
workers. We describe the important load-balancing features for handling graphs
with different characteristics. The design principles described in this paper
have been implemented in "GraphBLAST", the first high-performance linear
algebra-based graph framework on NVIDIA GPUs that is open-source. The results
show that on a single GPU, GraphBLAST has on average at least an order of
magnitude speedup over previous GraphBLAS implementations SuiteSparse and GBTL,
comparable performance to the fastest GPU hardwired primitives and
shared-memory graph frameworks Ligra and Gunrock, and better performance than
any other GPU graph framework, while offering a simpler and more concise
programming model.Comment: 50 pages, 14 figures, 14 table
Metastability-Containing Circuits
In digital circuits, metastability can cause deteriorated signals that
neither are logical 0 or logical 1, breaking the abstraction of Boolean logic.
Unfortunately, any way of reading a signal from an unsynchronized clock domain
or performing an analog-to-digital conversion incurs the risk of a metastable
upset; no digital circuit can deterministically avoid, resolve, or detect
metastability (Marino, 1981). Synchronizers, the only traditional
countermeasure, exponentially decrease the odds of maintained metastability
over time. Trading synchronization delay for an increased probability to
resolve metastability to logical 0 or 1, they do not guarantee success.
We propose a fundamentally different approach: It is possible to contain
metastability by fine-grained logical masking so that it cannot infect the
entire circuit. This technique guarantees a limited degree of metastability
in---and uncertainty about---the output.
At the heart of our approach lies a time- and value-discrete model for
metastability in synchronous clocked digital circuits. Metastability is
propagated in a worst-case fashion, allowing to derive deterministic
guarantees, without and unlike synchronizers. The proposed model permits
positive results and passes the test of reproducing Marino's impossibility
results. We fully classify which functions can be computed by circuits with
standard registers. Regarding masking registers, we show that they become
computationally strictly more powerful with each clock cycle, resulting in a
non-trivial hierarchy of computable functions
Cross-Sender Bit-Mixing Coding
Scheduling to avoid packet collisions is a long-standing challenge in
networking, and has become even trickier in wireless networks with multiple
senders and multiple receivers. In fact, researchers have proved that even {\em
perfect} scheduling can only achieve . Here
is the number of nodes in the network, and is the {\em medium
utilization rate}. Ideally, one would hope to achieve ,
while avoiding all the complexities in scheduling. To this end, this paper
proposes {\em cross-sender bit-mixing coding} ({\em BMC}), which does not rely
on scheduling. Instead, users transmit simultaneously on suitably-chosen slots,
and the amount of overlap in different user's slots is controlled via coding.
We prove that in all possible network topologies, using BMC enables us to
achieve . We also prove that the space and time
complexities of BMC encoding/decoding are all low-order polynomials.Comment: Published in the International Conference on Information Processing
in Sensor Networks (IPSN), 201
A Hybrid Approach to Formal Verification of Higher-Order Masked Arithmetic Programs
Side-channel attacks, which are capable of breaking secrecy via side-channel
information, pose a growing threat to the implementation of cryptographic
algorithms. Masking is an effective countermeasure against side-channel attacks
by removing the statistical dependence between secrecy and power consumption
via randomization. However, designing efficient and effective masked
implementations turns out to be an error-prone task. Current techniques for
verifying whether masked programs are secure are limited in their applicability
and accuracy, especially when they are applied. To bridge this gap, in this
article, we first propose a sound type system, equipped with an efficient type
inference algorithm, for verifying masked arithmetic programs against
higher-order attacks. We then give novel model-counting based and
pattern-matching based methods which are able to precisely determine whether
the potential leaky observable sets detected by the type system are genuine or
simply spurious. We evaluate our approach on various implementations of
arithmetic cryptographicprograms.The experiments confirm that our approach out
performs the state-of-the-art base lines in terms of applicability, accuracy
and efficiency
A Proposal for Dynamic Access Lists for TCP/IP Packet Filering
The use of IP filtering to improve system security is well established, and
although limited in what it can achieve has proved to be efficient and
effective.
In the design of a security policy there is always a trade-off between
usability and security. Restricting access means that legitimate use of the
network is prevented; allowing access means illegitimate use may be allowed.
Static access list make finding a balance particularly stark -- we pay the
price of decreased security 100% of the time even if the benefit of increased
usability is only gained 1% of the time.
Dynamic access lists would allow the rules to change for short periods of
time, and to allow local changes by non-experts. The network administrator can
set basic security guide-lines which allow certain basic services only. All
other services are restricted, but users are able to request temporary
exceptions in order to allow additional access to the network. These exceptions
are granted depending on the privileges of the user.
This paper covers the following topics: (1) basic introduction to TCP/IP
filtering; (2) semantics for dynamic access lists and; (3) a proposed protocol
for allowing dynamic access; and (4) a method for representing access lists so
that dynamic update and look-up can be done efficiently performed.Comment: 12 pages. Shortened version appeared in SAICSIT 200
A Type-Directed Negation Elimination
In the modal mu-calculus, a formula is well-formed if each recursive variable
occurs underneath an even number of negations. By means of De Morgan's laws, it
is easy to transform any well-formed formula into an equivalent formula without
negations -- its negation normal form. Moreover, if the formula is of size n,
its negation normal form of is of the same size O(n). The full modal
mu-calculus and the negation normal form fragment are thus equally expressive
and concise.
In this paper we extend this result to the higher-order modal fixed point
logic (HFL), an extension of the modal mu-calculus with higher-order recursive
predicate transformers. We present a procedure that converts a formula into an
equivalent formula without negations of quadratic size in the worst case and of
linear size when the number of variables of the formula is fixed.Comment: In Proceedings FICS 2015, arXiv:1509.0282
Automatic Integral Reduction for Higher Order Perturbative Calculations
We present a program for the reduction of large systems of integrals to
master integrals. The algorithm was first proposed by Laporta; in this paper,
we implement it in MAPLE. We also develop two new features which keep the size
of intermediate expressions relatively small throughout the calculation. The
program requires modest input information from the user and can be used for
generic calculations in perturbation theory.Comment: 23 page
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