Evaluación del rendimiento de un planificador de tareas sobre una plataforma heterogénea ARM+DSP de Texas Instruments

El presente trabajo estudia la viabilidad a la hora de aplicar un modelo de programación basado en la extracción de paralelismo a nivel de tareas sobre distintas arquitecturas heterogéneas basadas en un procesador multinúcleo de propósito general acelerado con uno o más aceleradores hardware. Se ha implementado una aplicación completa cuyo objetivo es la detección de bordes en una imagen (implementando el Algoritmo de Canny), y se ha evaluado en detalle su rendimiento sobre distintos tipos de arquitecturas, incluyendo CPUs multinúcleo de última generación, sistemas multi-GPU y una arquitectura objetivo basada en procesadores ARM Cortex-A15 acelerados mediante un DSP C66x de la compañía Texas Instruments. Los resultados experimentales demuestran la viabilidad de este tipo de implementación también para arquitecturas heterogéneas novedosas como esta última, e ilustran la facilidad de programación que introduce este tipo de modelos de programación sobre arquitecturas de propósito específico.

Fitness cost and interference of Arm/Rmt aminoglycoside resistance with the RsmF housekeeping methyltransferases

Arm/Rmt methyltransferases have emerged recently in pathogenic bacteria as enzymes that confer high-level resistance to 4,6-disubstituted aminoglycosides through methylation of the G1405 residue in the 16S rRNA (like ArmA and RmtA to -E). In prokaryotes, nucleotide methylations are the most common type of rRNA modification, and they are introduced posttranscriptionally by a variety of site-specific housekeeping enzymes to optimize ribosomal function. Here we show that while the aminoglycoside resistance methyltransferase RmtC methylates G1405, it impedes methylation of the housekeeping methyltransferase RsmF at position C1407, a nucleotide that, like G1405, forms part of the aminoglycoside binding pocket of the 16S rRNA. To understand the origin and consequences of this phenomenon, we constructed a series of in-frame knockout and knock-in mutants of Escherichia coli, corresponding to the genotypes rsmF(+), ΔrsmF, rsmF(+) rmtC(+), and ΔrsmF rmtC(+). When analyzed for the antimicrobial resistance pattern, the ΔrsmF bacteria had a decreased susceptibility to aminoglycosides, including 4,6- and 4,5-deoxystreptamine aminoglycosides, showing that the housekeeping methylation at C1407 is involved in intrinsic aminoglycoside susceptibility in E. coli. Competition experiments between the isogenic E. coli strains showed that, contrary to expectation, acquisition of rmtC does not entail a fitness cost for the bacterium. Finally, matrix-assisted laser desorption ionization (MALDI) mass spectrometry allowed us to determine that RmtC methylates the G1405 residue not only in presence but also in the absence of aminoglycoside antibiotics. Thus, the coupling between housekeeping and acquired methyltransferases subverts the methylation architecture of the 16S rRNA but elicits Arm/Rmt methyltransferases to be selected and retained, posing an important threat to the usefulness of aminoglycosides worldwide.