6,883 research outputs found
Emotional and Adrenocortical Responses of Infants to the Strange Situation: The Differential Function of Emotional Expression
The aim of the study was to investigate biobehavioural organisation in infants with different qualities of attachment. Quality of attachment (security and disorganisation), emotional expression, and adrenocortical stress reactivity were investigated in a sample of 106 infants observed during Ainsworth’s Strange Situation at the age of 12 months. In addition, behavioural inhibition was assessed from maternal reports. As expected, securely attached infants did not show an adrenocortical response. Regarding the traditionally defined insecurely attached groups, adrenocortical activation during the strange situation was found for the ambivalent group, but not for the avoidant one. Previous ndings of increased adrenocortical activity in disorganised infants could not be replicated. In line with previous ndings, adrenocortical activation was most prominent in insecure infants with high behavioural inhibition indicating the function of a secure attachment relationship as a social buffer against less adaptive temperamental dispositions. Additional analyses indicated that adrenocortical reactivity and behavioural distress were not based on common activation processes. Biobehavioural associations within the different attachment groups suggest that biobehavioural processes in securely attached infants may be different from those in insecurely attached and disorganised groups. Whereas a coping model may be applied to describe the biobehavioural organisation of secure infants, an arousal model explanation may be more appropriate for the other groups
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Graph prefetching using data structure knowledge
Searches on large graphs are heavily memory latency bound,
as a result of many high latency DRAM accesses. Due to
the highly irregular nature of the access patterns involved,
caches and prefetchers, both hardware and software, perform
poorly on graph workloads. This leads to CPU stalling for
the majority of the time. However, in many cases the data
access pattern is well defined and predictable in advance,
many falling into a small set of simple patterns. Although
existing implicit prefetchers cannot bring significant benefit,
a prefetcher armed with knowledge of the data structures
and access patterns could accurately anticipate applications'
traversals to bring in the appropriate data.
This paper presents a design of an explicitly configured
prefetcher to improve performance for breadth-first searches
and sequential iteration on the efficient and commonly-used
compressed sparse row graph format. By snooping L1 cache
accesses from the core and reacting to data returned from its
own prefetches, the prefetcher can schedule timely loads of
data in advance of the application needing it. For a range of
applications and graph sizes, our prefetcher achieves average
speedups of 2.3x, and up to 3.3x, with little impact on
memory bandwidth requirements.This work was supported by the Engineering and Physical
Sciences Research Council (EPSRC), through grant references EP/K026399/1 and EP/M506485/1, and ARM Ltd.This is the author accepted manuscript. The final version is available from ACM at http://dx.doi.org/10.1145/2925426.2926254
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Software prefetching for indirect memory accesses: A microarchitectural perspective
Many modern data processing and HPC workloads are heavily memory-latency bound. A tempting proposition to solve this is software prefetching, where special non-blocking loads are used to bring data into the cache hierarchy just before being required. However, these are difficult to insert to effectively improve performance, and techniques for automatic insertion are currently limited.
This article develops a novel compiler pass to automatically generate software prefetches for indirect memory accesses, a special class of irregular memory accesses often seen in high-performance workloads. We evaluate this across a wide set of systems, all of which gain benefit from the technique. We then evaluate the extent to which good prefetch instructions are architecture dependent and the class of programs that are particularly amenable. Across a set of memory-bound benchmarks, our automated pass achieves average speedups of 1.3× for an Intel Haswell processor, 1.1× for both an ARM Cortex-A57 and Qualcomm Kryo, 1.2× for a Cortex-72 and an Intel Kaby Lake, and 1.35× for an Intel Xeon Phi Knight’s Landing, each of which is an out-of-order core, and performance improvements of 2.1× and 2.7× for the in-order ARM Cortex-A53 and first generation Intel Xeon Phi.EPSRC [EP/K026399/1, EP/M506485/1], ARM Ltd
MarkUs: Drop-in use-after-free prevention for low-level languages
Use-after-free vulnerabilities have plagued software written in low-level languages, such as C and C++, becoming one of the most frequent classes of exploited software bugs. Attackers identify code paths where data is manually freed by the programmer, but later incorrectly reused, and take advantage by reallocating the data to themselves. They then alter the data behind the program’s back, using the erroneous reuse to gain control of the application and, potentially, the system. While a variety of techniques have been developed to deal with these vulnerabilities, they often have unacceptably high performance or memory overheads, especially in the worst case.
We have designed MarkUs, a memory allocator that prevents this form of attack at low overhead, sufficient for deployment in real software, even under allocation- and memory-intensive scenarios. We prevent use-after-free attacks by quarantining data freed by the programmer and forbidding its reallocation until we are sure that there are no dangling pointers targeting it. To identify these we traverse live-objects accessible from registers and memory, marking those we encounter, to check whether quarantined data is accessible from any currently allocated location. Unlike garbage collection, which is unsafe in C and C++, MarkUs ensures safety by only freeing data that is both quarantined by the programmer and has no identifiable dangling pointers. The information provided by the programmer’s allocations and frees further allows us to optimize the process by freeing physical addresses early for large objects, specializing analysis for small objects, and only performing marking when sufficient data is in quarantine. Using MarkUs, we reduce the overheads of temporal safety in low-level languages to 1.1× on average for SPEC CPU2006, with a maximum slowdown of only 2×, vastly improving upon the state-of-the-art.Arm Limite
Parallel error detection using heterogeneous cores
Microprocessor error detection is increasingly important, as the number of transistors in modern systems heightens their vulnerability. In addition, many modern workloads in domains such as the automotive and health industries are increasingly error intolerant, due to strict safety standards.
However, current detection techniques require duplication of all hardware structures, causing a considerable increase in power consumption and chip area. Solutions in the literature involve running the code multiple times on the same hardware, which reduces performance significantly and cannot capture all errors.
We have designed a novel hardware-only solution for error detection, that exploits parallelism in checking code which may not exist in the original execution. We pair a high-performance out-of-order core with a set of small low-power cores, each of which checks a portion of the out-of-order core's execution. Our system enables the detection of both hard and soft errors, with low area, power and performance overheads.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC), through grant references EP/K026399/1 and EP/M506485/1, and Arm Ltd
ParaMedic: Heterogeneous Parallel Error Correction
Processor error detection can be reduced in cost significantly by exploiting the parallelism that exists in a repeated copy of an execution, which may not exist in the original code, to split up the redundant work on a large number of small, highly efficient cores. However, such schemes don't provide a method for automatic error recovery.
We develop ParaMedic, an architecture to allow efficient automatic correction of errors detected in a system by using parallel heterogeneous cores, to provide a full fail-safe system that does not propagate errors to other systems, and can recover without manual intervention. This uses logging to roll back any computation that occurred after a detected error, along with a set of techniques to provide error-checking parallelism while still preventing the escape of incorrect processor values in multicore environments, where ordering of individual processors' logs is not enough to be able to roll back execution. Across a set of single and multi-threaded benchmarks, we achieve 3.1\% and 1.5\% overhead respectively, compared with 1.9\% and 1\% for error detection alone.Arm Lt
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The Guardian Council: Parallel programmable hardware security
Systems security is becoming more challenging in the face of untrusted programs and system users. Safeguards against attacks currently in use, such as buffer overflows, control-flow integrity, side channels and malware, are limited. Software protection schemes, while flexible, are often too expensive, and hardware schemes, while fast, are too constrained or out-of-date to be practical.
We demonstrate the best of both worlds with the Guardian Council, a novel parallel architecture to enforce a wide range of highly customisable and diverse security policies. We leverage heterogeneity and parallelism in the design of our system to perform security enforcement for a large high-performance core on a set of small microcontroller-sized cores. These Guardian Processing Elements (GPEs) are many orders of magnitude more efficient than conventional out-of-order superscalar processors, bringing high-performance security at very low power and area overheads. Alongside these highly parallel cores we provide fixed-function logging and communication units, and a powerful programming model, as part of an architecture designed for security.
Evaluation on a range of existing hardware and software protection mechanisms, reimplemented on the Guardian Council, across the SPEC CPU 2006 benchmarks demonstrates the flexibility of our approach with negligible overheads, out-performing prior work in the literature. For instance, 4 GPEs can provide forward control-flow integrity with 0% overhead, while 6 GPEs can provide a full shadow stack at only 2%.Arm Lt
Sub-arcsecond high sensitivity measurements of the DG~Tau jet with e-MERLIN
We present very high spatial resolution deep radio continuum observations at
5 GHz (6 cm) made with e-MERLIN of the young stars DG Tau A and B. Assuming it
is launched very close (~=1 au) from the star, our results suggest that the DG
Tau A outflow initially starts as a poorly focused wind and undergoes
significant collimation further along the jet (~=50 au). We derive jet
parameters for DG Tau A and find an initial jet opening angle of 86 degrees
within 2 au of the source, a mass-loss rate of 1.5x10^-8 solar masses/yr for
the ionised component of the jet, and the total ejection/accretion ratio to
range from 0.06-0.3. These results are in line with predictions from MHD
jet-launching theories.Comment: Accepted MNRAS Letter
Hematological response in sheep given protracted exposures to Co 60 gamma radiation
Leukocyte count changes in sheep after prolonged exposure to gamma irradiation at rate of 1.9 R/h
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