GPU Concurrency: Weak Behaviours and Programming Assumptions

Concurrency is pervasive and perplexing, particularly on graphics processing units (GPUs). Current specifications of languages and hardware are inconclusive; thus programmers often rely on folklore assumptions when writing software. To remedy this state of affairs, we conducted a large empirical study of the concurrent behaviour of deployed GPUs. Armed with litmus tests (i.e. short concurrent programs), we questioned the assumptions in programming guides and vendor documentation about the guarantees provided by hardware. We developed a tool to generate thousands of litmus tests and run them under stressful workloads. We observed a litany of previously elusive weak behaviours, and exposed folklore beliefs about GPU programming---often supported by official tutorials---as false. As a way forward, we propose a model of Nvidia GPU hardware, which correctly models every behaviour witnessed in our experiments. The model is a variant of SPARC Relaxed Memory Order (RMO), structured following the GPU concurrency hierarchy

O Sorriso da Avó em ‘Guarde Segredo’ de Esmeralda Ribeiro

No conto “Guarde Segredo” (1991), Esmeralda Ribeiro (1958-) substitui os pais “verdadeiros” ou biológicos de uma jovem afrodescendente por dois pais “falsos” (vovó Olívia e Lima Barreto). Por qual razão Ribeiro nos apresenta esta família alternativa? Neste artigo, defendo que a imaginação de uma nova família permite a Ribeiro combinar uma abordagem da invisibilidade literária, histórica e política das mulheres afrodescendentes com uma visão crítica e ambivalente da maternidade, quando esta se torna excessivamente visível na esfera privada. Apropriando-se dos princípios utilizados por sociedades disciplinares para regular relações raciais e sexuais, “Guarde Segredo” introduz estruturas panópticas de disciplina (Foucault, 1977) no cotidiano familiar dos inquilinos da casa situada à rua Major Mascarenhas, de modo a inverter o processo de invisibilidade crescente da jovem narradora, enquanto mãe afrodescendente em potência. A solução panóptica encontrada por Ribeiro cria uma plataforma privilegiada de acesso aos seus pais enquanto observadores/educadores, um dos quais é, como veremos, mais invisível do que o outro. A imaginação de uma nova família em “Guarde Segredo” permite a Ribeiro oferecer pistas teóricas necessárias para uma discussão sustentável e não essencialista da maternidade no contexto do projeto político-literário da escritura afro-brasileira

A derived transformation of emotional functions using self-reports, implicit association tests, and frontal alpha asymmetries

Research on the derived transformation of stimulus functions (ToF) typically employs single dependent measures for assessing the stimulus functions after derived relations have been established. For the first time, we examined ToF using three dependent measures both prior to and after relational training and testing. Specifically, we employed self-reports, implicit association tests, and frontal alpha asymmetry as pre versus post measures for assessing ToF. First, we trained two abstract shapes as contextual cues for happier-than and unhappier-than relations, respectively. Next, four conditional discriminations (A+/B–, B+/C–, C+/D–, and D+/E–) were trained in the presence of the happier-than cue only, where A, B, C, D, and E were blurred faces. This was followed by tests for contextually controlled transitive inference (TI) in the presence of both the happier-than and unhappier-than cues. For the participants who demonstrated TI, performance across all three measures following relational training and testing indicated that the Bhappiness^ functions of the A/B stimuli were greater than those of the D/E stimuli. This constitutes the first known demonstration of emotional ToF along explicit, implicit, and neurophysiological measures concurrently