Scalable i/o event handling for GHC

The Glasgow Haskell Compiler (GHC) is a well supported optimizing compiler for the Haskell programming language, along with its own extensions to the language and libraries. Haskell's lazy semantics imposes a runtime model which is in general difficult to implement efficiently. GHC achieves good performance across a wide variety of programs via aggressive optimization taking advantage of the lack of side effects, and by targeting a carefully tuned virtual machine. The Intel Labs Haskell Research Compiler uses GHC as a frontend, but provides a new whole-program optimizing backend by compiling the GHC intermediate representation to a relatively generic functional language compilation platform. We found that GHC's external Core language was relatively easy to use, but reusing GHC's libraries and achieving full compatibility were harder. For certain classes of programs, our platform provides substantial performance benefits over GHC alone, performing 2x faster than GHC with the LLVM backend on selected modern performance-oriented benchmarks; for other classes of programs, the benefits of GHC's tuned virtual machine continue to outweigh the benefits of more aggressive whole program optimization. Overall we achieve parity with GHC with the LLVM backend. In this paper, we describe our Haskell compiler stack, its implementation and optimization approach, and present benchmark results comparing it to GHC.

The Glasgow Haskell Compiler (GHC) has quite sophisticated support for concurrency in its runtime system, which is written in low-level C code. As GHC evolves, the runtime system becomes increasingly complex, error-prone, difficult to maintain and difficult to add new concurrency features.This paper presents an alternative approach to implement concurrency in GHC. Rather than hard-wiring all kinds of concurrency features, the runtime system is a thin substrate providing only a small set of concurrency primitives, and the remaining concurrency features are implemented in software libraries written in Haskell. This design improves the safety of concurrency support; it also provides more customizability of concurrency features, which can be developed as Haskell library packages and deployed modularly.

Expressing algorithms using immutable arrays greatly simplifies the challenges of automatic SIMD vectorization, since several important classes of dependency violations cannot occur. The Haskell programming language provides libraries for programming with immutable arrays, and compiler support for optimizing them to eliminate the overhead of intermediate temporary arrays. We describe an implementation of automatic SIMD vectorization in a Haskell compiler which gives substantial vector speedups for a range of programs written in a natural programming style. We compare performance with that of programs compiled by the Glasgow Haskell Compiler.

A limited form of dependent types, called Generalized Algebraic Data Types (GADTs), has recently been added to the list of Haskell extensions supported by the Glasgow Haskell Compiler. Despite not being full-fledged dependent types, GADTs still offer considerably enlarged scope for enforcing important code and data invariants statically. Moreover, GADTs offer the tantalizing possibility of writing more efficient programs since capturing invariants statically through the type system sometimes obviates entire layers of dynamic tests and associated data markup. This paper is a case study on the applications of GADTs in the context of Yampa, a domain-specific language for Functional Reactive Programming in the form of a self-optimizing, arrow-based Haskell combinator library. The paper has two aims. Firstly, to explore what kind of optimizations GADTs make possible in this context. Much of that should also be relevant for other domain-specific embedded language implementations, in particular arrow-based ones. Secondly, as the actual performance impact of the GADT-based optimizations is not obvious, to quantify this impact, both on tailored micro benchmarks, to establish the effectiveness of individual optimizations, and on two fairly large, realistic applications, to gauge the overall impact. The performance gains for the micro benchmarks are substantial. This implies that the Yampa API could be simplified as a number of "pre-composed" primitives that were there mainly for performance reasons are no longer needed. As to the applications, a worthwhile performance gain was obtained in one case whereas the performance was more or less unchanged in the other.

We describe a monadic interface to low-level hardware features that is a suitable basis for building operating systems in Haskell. The interface includes primitives for controlling memory management hardware, user-mode process execution, and low-level device I/O. The interface enforces memory safety in nearly all circumstances. Its behavior is specified in part by formal assertions written in a programming logic called P-Logic. The interface has been implemented on bare IA32 hardware using the Glasgow Haskell Compiler (GHC) runtime system. We show how a variety of simple O/S kernels can be constructed on top of the interface, including a simple separation kernel and a demonstration system in which the kernel, window system, and all device drivers are written in Haskell.

Arrows are a popular form of abstract computation. Being more general than monads, they are more broadly applicable, and, in particular, are a good abstraction for signal processing and dataflow computations. Most notably, arrows form the basis for a domain-specific language called Yampa , which has been used in a variety of concrete applications, including animation, robotics, sound synthesis, control systems, and graphical user interfaces. Our primary interest is in better understanding the class of abstract computations captured by Yampa. Unfortunately, arrows are not concrete enough to do this with precision. To remedy this situation, we introduce the concept of commutative arrows that capture a noninterference property of concurrent computations. We also add an init operator that captures the causal nature of arrow effects, and identify its associated law. To study this class of computations in more detail, we define an extension to arrows called causal commutative arrows (CCA), and study its properties. Our key contribution is the identification of a normal form for CCA called causal commutative normal form (CCNF). By defining a normalization procedure, we have developed an optimization strategy that yields dramatic improvements in performance over conventional implementations of arrows. We have implemented this technique in Haskell, and conducted benchmarks that validate the effectiveness of our approach. When compiled with the Glasgow Haskell Compiler (GHC), the overall methodology can result in significant speedups.

The most widely available high performance platforms today are multilevel clusters of multicores. The Glasgow Haskell Compiler (GHC) provides a number of parallel Haskell implementations targeting different parallel architectures. In particular, GHC-SMP supports shared memory, and GHC-GUM supports distributed memory machines. Both implementations use different, but related, runtime environment (RTE) mechanisms. Good performance results can be achieved on shared memory architectures and on networks individually. However, a combination of both, for networks of multicores, is lacking.We present the design and implementation of a new parallel Haskell RTE implementation, GUMSMP, which exploits hierarchical platforms more effectively. It is designed to efficiently combine distributed memory parallelism, using a virtual shared heap over a cluster, with low-overhead shared memory parallelism on the multicores. Key design objectives for realising this system are: asymmetric load balance, effective latency hiding, and mostly passive load distribution.We show that the automatic hierarchical load distribution policies must be carefully tuned to obtain good performance, showing the impact of several policies, including work pre-fetching and favouring inter-node work distribution. We present the initial performance results for this implementation, demonstrating the good scalability of a set of 8 benchmarks on up to 100 cores, and show performance gains of up to 20% compared to GHC-GUM.

Program power profiling based on phase behaviors

Multi-Version eXecution (MVX) is a technique that deploys many equivalent versions of the same program — variants — as a single program, with direct applications in important fields such as: security, reliability, analysis, and availability. MVX can be seen as “online Record/Replay (RR)”, as RR captures a program’s execution as a log stored on disk that can later be replayed to observe the same execution. Unfortunately, current MVX techniques target programs written in C/C++ and do not support programs written in managed languages, which are the vast majority of code written nowadays. This paper presents the design, implementation, and evaluation of Jmvx— a novel system for performing MVX and RR on programs written in managed languages. Jmvx supports programs written in Java by intercepting automatically identified non-deterministic methods, via a novel dynamic analysis technique, and ensuring that all variants execute the same methods and obtain the same data. Jmvx supports multi-threaded programs, by capturing synchronization operations in one variant, and ensuring all other variants follow the same ordering. We validated that Jmvx supports MVX and RR by applying it to a suite of benchmarks representative of programs written in Java. Internally, Jmvx uses a circular buffer located in shared memory between JVMs to enable fast communication between all variants, averaging 5% |47% performance overhead when performing MVX with multithreading support disabled|enabled, 8% |25% when recording, and 13% |73% when replaying.

Depression symptoms mediate the association between workplace stress and interleukin 6 in women, but not men: The Whitehall II study

Sixty-four children, aged 7 to 14 years, with early-treated PKU, were compared with control children on visual evoked potential (VEP) amplitudes and latencies and auditory mismatch negativity (MMN) amplitudes. It was further investigated whether indices of dietary control would be associated with these evoked potentials parameters. There were no significant differences between controls and children with PKU in VEP- and MMN-indices. However, higher lifetime Phe levels were, in varying degree and stronger than concurrent Phe level, related to increased N75 amplitudes, suggesting abnormalities in attention, and longer P110 latencies, indicating a reduction in speed of neural processing, possibly due to deficits in myelination or reduced dopamine levels in brain and retina. Similarly, higher lifetime Phe levels and Index of Dietary Control (IDC) were associated with decreased MMN amplitudes, suggesting a reduced ability to respond to stimulus change and poorer triggering of the frontally mediated attention switch. In summary, the present study in children with PKU investigated bottom-up information processing, i.e., triggered by external events, a fundamental prerequisite for the individual’s responsiveness to the outside world. Results provide evidence that quality of dietary control may affect the optimal development of these pre-attentive processes, and suggest the existence of windows of vulnerability to Phe exposure.

Event-related potential correlates of selective processing in early- and continuously-treated children with phenylketonuria: Effects of concurrent phenylalanine level and dietary control

ABSTRACTBackground: There is a growing body of research linking sedentary behavior with increased risk of chronic disease and all-cause mortality. It is increasingly recommended that service providers address the multiple behavioral risk factors associated with these chronic diseases as part of routine substance abuse treatment. Objectives: The study objective was to investigate rates of physical activity and sedentary behavior in a residential substance abuse population. In addition, efficacy of a sedentary behavior intervention, “Sit Switch,” was examined for feasibility in this context. Methods: Participants (n = 54) were residents of The Salvation Army Recovery Service Centres located in Canberra and on the Gold Coast, Australia. Actigraph GT3X+ accelerometers were used to measure rates and patterns of sedentariness and physical activity. A nonrandomized controlled study of a single-session group intervention aimed at decreasing prolonged sitting (“Sit Switch”) was conducted. Education, motivational-interviewing, and goal setting components underpinned the “Sit Switch” intervention. Results: Individuals were highly sedentary, spending 73% of daily activity at sedentary intensity engaged in inadequate levels of moderate physical activity (6.6%/day). The single session educational program did not lead to any significant changes in sedentary behavior. Conclusion/Importance: High levels of sedentariness and low levels of physical activity engagement are evident in residents in substance abuse treatment programs. It is strongly recommended that sedentariness, a modifiable risk behavior with independent consequences for cardiovascular disease and cancer, be addressed within residential programs.

Effective socialization of new student affairs professionals is essential both for the individual success of these practitioners, and for the work of a college or university that promotes student learning. It enables new professionals to manage the important personal and professional transitions they experience throughout their careers, engage in continuous professional development, and achieve high levels of productivity. It also counteracts the high attrition rate among new hires, with all the attendant costs to the institution in terms of resources spent on recruiting, hiring, training, supervising, and developing staff talent.The socialization process for new professionals includes formal and informal elements that influence both success and quality of work life. This process is far more complex than a single orientation program organized by a unit or division. Rather, it is a comprehensive process where both the new professional and organization learn about and from each other in ways that influence working relationships and individual and organizational outcomes.Part I of this book defines the concept, explains its value, and offers a model of socialization. Part II examines the institutional context in which the socialization of new professionals occurs, and describes how different institutional types influence the socialization process. It considers the changing characteristics of college students, and how these impact the work of student affairs.In addressing the extra-institutional and professional contexts, Part III considers the role that graduate education plays in preparing new professionals for work in student affairs, and offers guidance to faculty and practitioners involved in graduate education about what they can do to introduce graduate students to professional life. It addresses the importance of professional orientation activities, the roles of supervision and mentorship, as well as the impact of peers and institutions on the socialization process. It concludes with a discussion of the role and importance of professional associations.This book is intended for graduate program faculty, for senior student affairs officers concerned about developing and retaining the new staff, and for administrators and leaders in student affairs shaping the future of the profession. For new professionals themselves it offers insights on the path to professionalization.

Recent studies by economists such as Piketty (2013, 2019) and Atkinson (2015) have contested the well-established view that post-war redistribution policies have been successful in the long term at slowing down the rise of structural inequalities. In reality, the claim goes, they have dealt mostly with reducing inequalities of income through redistribution and have left inequalities of wealth and capital ownership uncontrolled. These, according to their studies, have now risen in the developed world and reached levels more typical of 19th Century Europe. To make matters worse, perceptions of and attitudes towards fighting inequalities as unjust that Rawls saw as based on a wide consensus of citizens' "considered judgments" (Rawls, 1999, p. 17), have changed, leading to them being accepted as the justified and even necessary price to pay for economic growth and as a reward for merit. Economic arguments based on the need for incentives for raising productivity and the "trickle-down effect" have become widely accepted as if the price of economic efficiency should be disconnected from the demands of equity. Meritocracy has provided ethical arguments too. As John Roemer says, "today the most important problem for the social sciences of inequality is understanding how electorates have come to acquiesce to policies which increase inequality… and to try revealing the logic of the I would like to thank the editors of the Special Issue on Rawls for inviting me to develop ideas that I first presented in a previous paper published in French in 2016, "L'état-providence face aux inégalités et la démocratie de propriétaires: une comparaison entre Meade, Rawls, Ackerman et Piketty," Tocqueville Review, 2/2016), as well as in another paper in English in 2018: « Self-development and Social Justice ». I hope to be able to develop these ideas in a future book on property-owning democracy and its philosophical justifications.