Fastpass: A Centralized “Zero-Queue” Datacenter Network

An ideal datacenter network should provide several properties, including low median and tail latency, high utilization (throughput), fair allocation of network resources between users or applications, deadline-aware scheduling, and congestion (loss) avoidance. Current datacenter networks inherit the principles that went into the design of the Internet, where packet transmission and path selection decisions are distributed among the endpoints and routers. Instead, we propose that each sender should delegate control—to a centralized arbiter—of when each packet should be transmitted and what path it should follow. This paper describes Fastpass, a datacenter network architecture built using this principle. Fastpass incorporates two fast algorithms: the first determines the time at which each packet should be transmitted, while the second determines the path to use for that packet. In addition, Fastpass uses an efficient protocol between the endpoints and the arbiter and an arbiter replication strategy for fault-tolerant failover. We deployed and evaluated Fastpass in a portion of Facebook’s datacenter network. Our results show that Fastpass achieves high throughput comparable to current networks at a 240 reduction is queue lengths (4.35 Mbytes reducing to 18 Kbytes), achieves much fairer and consistent flow throughputs than the baseline TCP (5200 reduction in the standard deviation of per-flow throughput with five concurrent connections), scalability from 1 to 8 cores in the arbiter implementation with the ability to schedule 2.21 Terabits/s of traffic in software on eight cores, and a 2.5 reduction in the number of TCP retransmissions in a latency-sensitive service at Facebook.National Science Foundation (U.S.) (grant IIS-1065219)Irwin Mark Jacobs and Joan Klein Jacobs Presidential FellowshipHertz Foundation (Fellowship

Flowtune: Flowlet Control for Datacenter Networks

Rapid convergence to a desired allocation of network resources to endpoint traffic has been a long-standing challenge for packet-switched networks. The reason for this is that congestion control decisions are distributed across the endpoints, which vary their offered load in response to changes in application demand and network feedback on a packet-by-packet basis. We propose a different approach for datacenter networks, flowlet control, in which congestion control decisions are made at the granularity of a flowlet, not a packet. With flowlet control, allocations have to change only when flowlets arrive or leave. We have implemented this idea in a system called Flowtune using a centralized allocator that receives flowlet start and end notifications from endpoints. The allocator computes optimal rates using a new, fast method for network utility maximization, and updates endpoint congestion-control parameters. Experiments show that Flowtune outperforms DCTCP, pFabric, sfqCoDel, and XCP on tail packet delays in various settings, converging to optimal rates within a few packets rather than over several RTTs. Our implementation of Flowtune handles 10.4x more throughput per core and scales to 8x more cores than Fastpass, for an 83-fold throughput gain

Photonic Interconnection Networks for Exascale Computers

[ES] En los últimos años, distintos proyectos alrededor del mundo se han centrado en el diseño de supercomputadores capaces de alcanzar la meta de la computación a exascala, con el objetivo de soportar la ejecución de aplicaciones de gran importancia para la sociedad en diversos campos como el de la salud, la inteligencia artificial, etc. Teniendo en cuenta la creciente tendencia de la potencia computacional en cada generación de supercomputadores, este objetivo se prevee accesible en los próximos años. Alcanzar esta meta requiere abordar diversos retos en el diseño y desarrollo del sistema. Uno de los principales es conseguir unas comunicaciones rápidas y eficientes entre el inmenso número de nodos de computo y los sitemas de memoria. La tecnología fotónica proporciona ciertas ventajas frente a las redes eléctricas, como un mayor ancho de banda en los enlaces, un mayor paralelismo a nivel de comunicaciones gracias al DWDM o una mejor gestión del cableado gracias a su reducido tamaño. En la tesis se ha desarrollado un estudio de viabilidad y desarrollo de redes de interconexión haciendo uso de la tecnología fotónica para los futuros sistemas a exaescala dentro del proyecto europeo ExaNeSt. En primer lugar, se ha realizado un análisis y caracterización de aplicaciones exaescala. Este análisis se ha utilizado para conocer el comportamiento y requisitos de red que presentan las aplicaciones, y con ello guiarnos en el diseño de la red del sistema. El análisis considera tres parámetros: la distribución de mensajes en base a su tamaño y su tipo, el consumo de ancho de banda requerido a lo largo de la ejecución y la matriz de comunicación espacial entre los nodos. El estudio revela la necesidad de una red eficiente y rápida, debido a que la mayoría de las comunaciones se realizan en burst y con mensajes de un tamaño medio inferior a 50KB. A continuación, la tesis se centra en identificar los principales elementos que diferencian las redes fotónicas de las eléctricas. Identificamos una secuencia de pasos en el diseño de un simulador, ya sea haciéndolo desde cero con tecnología fotónica o adaptando un simulador de redes eléctricas existente para modelar la fotónica. Después se han realizado dos estudios de rendimiento y comparativas entre las actuales redes eléctricas y distintas configuraciones de redes fotónicas utilizando topologías clásicas. En el primer estudio, realizado tanto con tráfico sintético como con trazas de ExaNeSt en un toro, fat tree y dragonfly, se observa como la tecnología fotónica supone una clara mejora respecto a la eléctrica. Además, el estudio muestra que el parámetro que más afecta al rendimiento es el ancho de banda del canal fotónico. El segundo estudio muestra el comportamiento y rendimiento de aplicaciones reales en simulaciones a gran escala en una topología jellyfish. En este estudio se confirman las conclusiones obtenidas en el anterior, revelando además que la tecnología fotónica permite reducir la complejidad de algunas topologías, y por ende, el coste de la red. En los estudios realizados se ha observado una baja utilización de la red debido a que las topologías utilizadas para redes eléctricas no aprovechan las características que proporciona la tecnología fotónica. Por ello, se ha propuesto Segment Switching, una estrategia de conmutación orientada a reducir la longitud de las rutas mediante el uso de buffers intermedios. Los resultados experimentales muestran que cada topología tiene sus propios requerimientos. En el caso del toro, el mayor rendimiento se obtiene con un mayor número de buffers en la red. En el fat tree el parámetro más importante es el tamaño del buffer, obteniendo unas prestaciones similares una configuración con buffers en todos los switches que la que los ubica solo en el nivel superior. En resumen, esta tesis estudia el uso de la tecnología fotónica para las redes de sistemas a exascala y propone aprovechar[CA] Els darrers anys, múltiples projectes de recerca a tot el món s'han centrat en el disseny de superordinadors capaços d'assolir la barrera de computació exascala, amb l'objectiu de donar suport a l'execució d'aplicacions importants per a la nostra societat, com ara salut, intel·ligència artificial, meteorologia, etc. Segons la tendència creixent en la potència de càlcul en cada generació de superordinadors, es preveu assolir aquest objectiu en els propers anys. No obstant això, assolir aquest objectiu requereix abordar diferents reptes importants en el disseny i desenvolupament del sistema. Un dels principals és aconseguir comunicacions ràpides i eficients entre l'enorme nombre de nodes computacionals i els sistemes de memòria. La tecnologia fotònica proporciona diversos avantatges respecte a les xarxes elèctriques actuals, com ara un major ample de banda als enllaços, un major paral·lelisme de la xarxa gràcies a DWDM o una millor gestió del cable a causa de la seva mida molt més xicoteta. En la tesi, s'ha desenvolupat un estudi de viabilitat i desenvolupament de xarxes d'interconnexió mitjançant tecnologia fotònica per a futurs sistemes exascala dins del projecte europeu ExaNeSt. En primer lloc, s'ha dut a terme un estudi de caracterització d'aplicacions exascala dels requisits de xarxa. Els resultats de l'anàlisi ajuden a entendre els requisits de xarxa de les aplicacions exascale i, per tant, ens guien en el disseny de la xarxa del sistema. Aquesta anàlisi considera tres paràmetres principals: la distribució dels missatges en funció de la seva mida i tipus, el consum d'ample de banda requerit durant tota l'execució i els patrons de comunicació espacial entre els nodes. L'estudi revela la necessitat d'una xarxa d'interconnexió ràpida i eficient, ja que la majoria de comunicacions consisteixen en ràfegues de transmissions, cadascuna amb una mida mitjana de missatge de 50 KB. A continuació, la tesi se centra a identificar els principals elements que diferencien les xarxes fotòniques de les elèctriques. Identifiquem una seqüència de passos en el disseny i implementació d'un simulador: tractar la tecnologia fotònica des de zero o per ampliar un simulador de xarxa elèctrica existent per modelar la fotònica. Després, es presenten dos estudis principals de comparació de rendiment entre xarxes elèctriques i diferents configuracions de xarxes fotòniques mitjançant topologies clàssiques. En el primer estudi, realitzat tant amb trànsit sintètic com amb traces d'ExaNeSt en un toro, fat tree i dragonfly, vam trobar que la tecnologia fotònica representa una millora notable respecte a la tecnologia elèctrica. A més, l'estudi mostra que el paràmetre que més afecta el rendiment és l'amplada de banda del canal fotònic. Aquest darrer estudi analitza el rendiment d'aplicacions reals en simulacions a gran escala en una topologia jellyfish. Els resultats d'aquest estudi corroboren les conclusions obtingudes en l'anterior, revelant també que la tecnologia fotònica permet reduir la complexitat d'algunes topologies i, per tant, el cost de la xarxa. En els estudis anteriors ens adonem que la xarxa estava infrautilitzada principalment perquè les topologies estudiades per a xarxes elèctriques no aprofiten les característiques proporcionades per la tecnologia fotònica. Per aquest motiu, proposem Segment Switching, una estratègia de commutació destinada a reduir la longitud de les rutes mitjançant la implementació de memòries intermèdies en nodes intermedis al llarg de la ruta. Els resultats experimentals mostren que cadascuna de les topologies estudiades presenta diferents requisits de memòria intermèdia. Per al toro, com més gran siga el nombre de memòries intermèdies a la xarxa, major serà el rendiment. Per al fat tree, el paràmetre clau és la mida de la memòria intermèdia, aconseguint un rendiment similar tant amb una configuració amb memòria intermèdia en tots els co[EN] In the last recent years, multiple research projects around the world have focused on the design of supercomputers able to reach the exascale computing barrier, with the aim of supporting the execution of important applications for our society, such as health, artificial intelligence, meteorology, etc. According to the growing trend in the computational power in each supercomputer generation, this objective is expected to be reached in the coming years. However, achieving this goal requires addressing distinct major challenges in the design and development of the system. One of the main ones is to achieve fast and efficient communications between the huge number of computational nodes and the memory systems. Photonics technology provides several advantages over current electrical networks, such as higher bandwidth in the links, greater network parallelism thanks to DWDM, or better cable management due to its much smaller size. In this thesis, a feasibility study and development of interconnection networks have been developed using photonics technology for future exascale systems within the European project ExaNeSt. First, a characterization study of exascale applications from the network requirements has been carried out. The results of the analysis help understand the network requirements of exascale applications, and thereby guide us in the design of the system network. This analysis considers three main parameters: the distribution of the messages based on their size and type, the required bandwidth consumption throughout the execution, and the spatial communication patterns between the nodes. The study reveals the need for a fast and efficient interconnection network, since most communications consist of bursts of transmissions, each with an average message size of 50 KB. Next, this dissertation concentrates on identifying the main elements that differentiate photonic networks from electrical ones. We identify a sequence of steps in the design and implementation of a simulator either i) dealing with photonic technology from scratch or ii) to extend an existing electrical network simulator in order to model photonics. After that, two main performance comparison studies between electrical networks and different configurations of photonic networks are presented using classical topologies. In the former study, carried out with both synthetic traffic and traces of ExaNeSt in a torus, fat tree and dragonfly, we found that photonic technology represents a noticeable improvement over electrical technology. Furthermore, the study shows that the parameter that most affects the performance is the bandwidth of the photonic channel. The latter study analyzes performance of real applications in large-scale simulations in a jellyfish topology. The results of this study corroborates the conclusions obtained in the previous, also revealing that photonic technology allows reducing the complexity of some topologies, and therefore, the cost of the network. In the previous studies we realize that the network was underutilized mainly because the studied topologies for electrical networks do not take advantage of the features provided by photonic technology. For this reason, we propose Segment Switching, a switching strategy aimed at reducing the length of the routes by implementing buffers at intermediate nodes along the path. Experimental results show that each of the studied topologies presents different buffering requirements. For the torus, the higher the number of buffers in the network, the higher the performance. For the fat tree, the key parameter is the buffer size, achieving similar performance a configuration with buffers on all switches that locating buffers only at the top level. In summary, this thesis studies the use of photonic technology for networks of exascale systems, and proposes to take advantage of the characteristics of this technology in current electrical network topologies.This thesis has been conceived from the work carried out by Polytechnic University of Valencia in the ExaNeSt European projectDuro Gómez, J. (2021). Photonic Interconnection Networks for Exascale Computers [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/166796TESI

The Genetic, Molecular, And Cellular Bases Of Unidentified Primary Immunodeficiencies

The immune system is inseparable from every part of human biology. From cell intrinsic mechanisms of pathogen recognition to multi-cellular interactions over vast ranges of time and space, the immune system is both essential for protection from infection and central to the pathogenesis of many diseases. Thus understanding it has long been a focus of biomedical research. While in vitro molecular, biochemical, and cellular techniques as well as complex genetically modified animal models have been developed, these approaches still only approximate true human disease and in vivo human biology. Primary immunodeficiencies are inborn genetic defects of immunity and present rare opportunities to observe, study, and understand how genetic perturbations impact human immunity directly. I therefore clinically and genetically analyzed three patient families with unidentified primary immunodeficiencies. Using whole exome sequencing coupled with in vitro and in vivo biochemical and cellular assays, I identified two novel genetic etiologies of primary immunodeficiency. I first identified de novo missense mutations in GNAI2, the gene encoding the ubiquitously expressed heterotrimeric G-protein Gαi2, in 2 families with life-threating multi-organ system autoimmunity and immunodeficiency to mucocutaneous infections. Gαi2 is essential for chemokine mediated leukocyte migration as well as regulating development, inflammation, and metabolism in the immune system and beyond. The heterozygous dominant gain-of-function patient proteins impaired chemokine signaling and chemotaxis in addition to augmenting T cell activation by constitutively activating costimulatory pathways and reducing the requirement for T cell costimulation. I also identified homozygous missense mutations in IFIH1, the gene encoding the cytosolic pattern recognition receptor of dsRNA MDA5, in the third family of study. The affected individual presented with recurrent severe respiratory infections with RNA viruses including human rhinovirus, coronaviruses (HKU1, OC43, NL63), influenza virus, and respiratory syncytial virus. The mutant protein lost the ability to bind dsRNA and failed to initiate antiviral interferon-β and pro-inflammatory NF-κB responses. Using gene knockdown and gene editing in immortalized and patient derived cell lines, I demonstrated an essential role for MDA5 in restricting rhinovirus infection in human respiratory epithelium. Thus this work demonstrates the power of human genetics to identify disease causing mutations in rare individuals and reveal how the immune system uses molecules involved in cell migration, activation, and nucleic acid sensing to robustly protect us from virus infections without causing autoimmunity

ACTIVITY-DEPENDENT CHANGES IN A NEURONAL CIRCUIT IMPORTANT FOR SOUND LOCALIZATION

Aside from recognizing and distinguishing sound patterns, the ability to localize sounds in the horizontal plane is an essential component of the mammalian auditory system. It facilitates approaching potential mating partners and allows avoiding predators. The superior olivary complex (SOC) within the auditory brainstem is the first site of binaural interaction and its major projections and inputs are well investigated. The adult input pattern, however, is not set from the beginning but changes over the period of development. Mammals including humans experience different stages and conditions of hearing during auditory development. The human brain for instance has to perform a transition after birth from the perception of sound waves transmitted in amniotic fluid to the perception of airborne sounds. Furthermore, small mammals like rodents, which are common model organisms for auditory research, perceive airborne sounds for the first time some days after birth, when their ear canals open. The basic neuronal projections and the intrinsic properties of neurons, such as the expression of specific ion channels, are already established and adjusted in the SOC during the perinatal period of partial deafness. An additional refinement of inputs and further adaptations of intrinsic characteristics occur with the onset of hearing in response to the new acoustic environment. It is likely that with ongoing maturation well-established inputs within the sound localization network need these adaptations to balance anatomical changes such as an increasing head size. In addition, short-term adjustments of synaptic inputs in the adult auditory system are equally necessary for a faithful representation of auditory space. A recent study suggests that these short-term adaptations are partially represented at the auditory brainstem level. The question of how intrinsic properties change during auditory development, to what extent auditory experience is involved in these changes and the functional implications of these changes on the sound localization circuitry is only partially answered. I used the hyperpolarization-activated and cyclic nucleotide-gated cation channels (HCN channels), which are a key determinant of the intrinsic properties of auditory brainstem neurons, as a target to study the influence of auditory experience on the intrinsic properties of neurons in the auditory brainstem. Another important question still under discussion is how neurons in the auditory brainstem might fine-tune their firing behavior to cope optimally with an altered acoustic environment. Recent data suggest that auditory processing is also affected by modulatory mechanisms at the brainstem level, which for instance change the input strength and thus alter the spike output of these neurons. One possible candidate is the metabotropic GABAB receptor (GABABR) which has been shown to be abundant in the adult auditory brainstem, although GABAergic projections are scarce in the mature auditory brainstem. These questions were investigated by performing whole-cell patch-clamp recordings of SOC neurons from Mongolian gerbils at different developmental stages in the acute brain slice preparation. Specific currents and receptors were isolated using pharmacological means. Immmunohistochemical results additionally supported physiological findings. In the first study, I investigated the developmental regulation of HCN channels in the SOC and their underlying depolarizing current Ih, which has been shown to regulate the excitability of neurons and to enhance the temporally precise analysis of binaural acoustic cues. I characterized the developmental changes of Ih in neurons of the lateral superior olive (LSO) and the medial nucleus of the trapezoid body (MNTB), which in the adult animals show different HCN subunit composition. I showed that right after hearing onset there was a strong increase of Ih in the LSO and just a minor increase in the MNTB. In addition, the open probability of HCN channels was shifted towards more positive voltages in both nuclei and the activation time constants accelerated during the first days of auditory experience. These results implicate that Ih is actively regulated by sensory input activity. I tested this hypothesis by inducing auditory deprivation which was achieved by surgically removing the cochlea in gerbils before hearing onset. The effect was opposite in neurons of the MNTB and the LSO. Whereas in LSO neurons auditory deprivation resulted in increased Ih amplitude, MNTB neurons displayed a moderate decrease in Ih. These results suggest that auditory experience differentially changes the amount of HCN channels dependent on the subunit composition or possibly alters intracellular cAMP levels, thereby shifting the voltage dependence of Ih. This regulatory mechanism might thus maintain adequate excitability levels within the SOC. A second study was carried out to investigate the role of GABABRs in the medial superior olive (MSO). Upon activation, these metabotropic receptors are known to decrease the release probability of neurotransmitters at the presynapse thereby altering excitatory and inhibitory currents at the postsynaptic site. Neurons in the MSO analyze interaural time differences (ITDs) by comparing the relative timing of the excitatory inputs from the two ears using a coincidence mechanism. In addition, these neurons receive a precisely timed inhibitory input from each ear which shifts ITDs in the physiological relevant range. Since the major inhibitory input changes its transmitter type from mixed GABA/glycinergic to only glycinergic after hearing onset it was now interesting to examine the mediated effects of GABABRs, which have been shown to be abundant in the prehearing and adult MSO of gerbils. Furthermore, revealing the precise expression pattern of GABABRs and their influence on excitatory and inhibitory currents in the MSO during auditory development should provide further evidence of their functional relevance. Performing pharmacological experiments I could now demonstrate that the activation of GABABRs before hearing onset decreases the current of excitatory inputs stronger than that of inhibitory inputs whereas a switch is performed after hearing onset and inhibitory currents are stronger decreasedcompared to excitatory currents. In a similar way, also the expression pattern of GABABRs changes before and after hearing onset as revealed by immunohistochemistry. Since the main inhibitory inputs to the adult MSO are purely glycinergic, it was commonly assumed that GABABRs occupy only a minor role in the mature auditory brainstem. Contradictory to this, it was possible to activate presynaptic GABABRs by synaptic stimulation even in adult animals and to observe a profound decrease of inhibitory current in MSO neurons. These results suggest GABAergic projections of yet unknown origin targeting the MSO. It is therefore quite likely that GABABRs modulate and possibly improve the localization of low frequency sounds even in adult mammals. Summarized, the outcome of this thesis contributes to a better understanding of the developmental adaptation in the auditory system and demonstrates that the orderly specification of intrinsic properties within the SOC is dependent on auditory experience. Moreover, I show that even in mature animals the synaptic strength of MSO inputs can be modulated by synaptic GABA release. This should emphasize the importance of modulatory mechanisms and could be the basis for future studies concerning the field of sound localization

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Spartan Daily, February 5, 1982

Volume 78, Issue 3https://scholarworks.sjsu.edu/spartandaily/6846/thumbnail.jp