Efficient techniques to provide scalability for token-based cache coherence protocols

Cache coherence protocols based on tokens can provide low latency without relying on non-scalable interconnects thanks to the use of efficient requests that are unordered. However, when these unordered requests contend for the same memory block, they may cause protocols races. To resolve the races and ensure the completion of all the cache misses, token protocols use a starvation prevention mechanism that is inefficient and non-scalable in terms of required storage structures and generated traffic. Besides, token protocols use non-silent invalidations which increase the latency of write misses proportionally to the system size. All these problems make token protocols non-scalable. To overcome the main problems of token protocols and increase their scalability, we propose a new starvation prevention mechanism named Priority Requests. This mechanism resolves contention by an efficient, elegant, and flexible method based on ordered requests. Furthermore, thanks to Priority Requests, efficient techniques can be applied to limit the storage requirements of the starvation prevention mechanism, to reduce the total traffic generated for managing protocol races, and to reduce the latency of write misses. Thus, the main problems of token protocols can be solved, which, in turn, contributes to wide their efficiency and scalability.Cuesta Sáez, BA. (2009). Efficient techniques to provide scalability for token-based cache coherence protocols [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/6024Palanci

Switch-based packing technique to reduce traffic and latency in token coherence

Token Coherence is a cache coherence protocol able to simultaneously capture the best attributes of traditional protocols: low latency and scalability. However it may lose these desired features when (1) several nodes contend for the same memory block and (2) nodes write highly-shared blocks. The first situation leads to the issue of simultaneous broadcast requests which threaten the protocol scalability. The second situation results in a burst of token responses directed to the writer, which turn it into a bottleneck and increase the latency. To address these problems, we propose a switch-based packing technique able to encapsulate several messages (while in transit) into just one. Its application to the simultaneous broadcasts significantly reduces their bandwidth requirements (up to 45%). Its application to token responses lowers their transmission latency (by 70%). Thus, the packing technique decreases both the latency and coherence traffic, thereby improving system performance (about 15% of reduction in runtime). © 2011 Elsevier Inc. All rights reserved.This work was partially supported by the Spanish MEC and MICINN, as well as European Commission FEDER funds, under Grants CSD2006-00046 and TIN2009-14475-C04-01.Cuesta Sáez, BA.; Robles Martínez, A.; Duato Marín, JF. (2012). Switch-based packing technique to reduce traffic and latency in token coherence. Journal of Parallel and Distributed Computing. 72(3):409-423. https://doi.org/10.1016/j.jpdc.2011.11.010S40942372

Construcción de formas libres a partir de modelos: análisis de los métodos experimentales de Heinz Isler, su eficiencia y sostenibilidad

169 p.El descubrimiento del hormigón armado despertó en algunos arquitectos e ingenieros del siglo XX especial interés por la construcción de superficies laminares. Las características de este material propiciaban cáscaras estructuralmente eficientes. Sin embargo, sus diseños se vieron limitados por la complejidad matemática que presentaba la Teoría de la Membrana (1908). El ingeniero suizo Heinz Isler (1926-2009) construyó este tipo de estructuras desligándose de la rigidez que ofrecía el cálculo elástico. Gracias a su admiración por la naturaleza y desde una perspectiva lúdica y experimental, este ingeniero desarrolló un sistema eficiente con el que liberó el diseño de las cáscaras. El proceso partía de la búsqueda formal de láminas estructuralmente eficientes basándose en tres métodos físicos distintos. Con el primero de ellos diseñó cáscaras inspiradas en pañuelos colgados, traccionados por la gravedad. Posteriormente se invertían, trabajando a compresión pura (modelos de membrana colgada invertida). El segundo método se basó en cojines y pompas. Las formas de estos elementos eran el resultado de la expansión producida por sus tensiones internas. Estas fuerzas fueron sustituidas por el peso propio de las cubiertas, pasando entonces a trabajar a compresión (modelo “Bubble Shells”). El último método que propuso Heinz Isler se apoyó en formas de crecimiento natural en expansión (modelos de forma libre). El trabajo consta de dos partes. En la primera se hace una revisión sobre los referentes directos de Isler. También se expone el sistema innovador “Form-finding” que desarrolló este ingeniero y la acogida de los tres modelos mencionados anteriormente que presentó en el Primer Congreso de la IASS de 1959. La segunda parte determina el comportamiento estructural y los aspectos formales que caracterizan a cada uno de estos tres métodos. Se ha comparado mediante análisis gráficos la adecuación y las ventajas de cada uno de ellos atendiendo a cuestiones estructurales, sostenibles, espaciales, económicas y formales.The discovery of reinforced concrete aroused the interest of some 20th century architects and engineers in the construction of lamellar structures. The properties of this material provided structurally efficient shells. However, their designs were limited by the mathematical complications of the Membrane Theory (1908). The Swiss engineer Heinz Isler (1926-2009) built such structures by distancing himself from the rigidity offered by elastic analysis. Thanks to his admiration for Nature and from a playful and experimental approach, this engineer developed an efficient system with which he unleashed the design of the shells. The process started with the formal search for structurally efficient shells based on three different physical methods. In the first one, he designed shells inspired on hanging cloths, pulled by gravity. They were then inverted, performing under pure compression (hanging cloth reversed model). The second method was based on pillows and bubbles. The shapes of these elements were the result of the expansion produced by their internal stresses. These forces were substituted by the self-weight of the shells, so that they started to perform in compression (“Bubble Shells” model). The last of Heinz Isler’s methods was derived from natural growing forms in expansion (free-form models). The project consists of two parts. The first one reviews Isler’s immediate references. It also presents the innovative “Form-finding” system developed by this engineer and the reception of the three models mentioned above, presented at the First IASS Congress in 1959. The second part determines the structural behaviour and formal aspects that characterize each of these three methods. The adequacy and advantages of each method have been compared through graphic analysis, considering structural, environmental, spatial, economical and formal issues.Grado en Fundamentos de Arquitectura y Urbanism

Effect of early feed restriction on performance and health status in growing rabbits slaughtered at 2 kg live-weight

[EN] The effect of a time-limited access to the feeders (8 h per d from 9:30 to 17:30) on fattening performance and health status was studied in rabbits reared until 2 kg live-weight as typical in the Spanish market. For this purpose, the same diet (10.5 MJ digestible energy/kg, 38.9% neutral detergent fibre and 18.4% crude protein on dry matter basis) was used over two consecutive trials. A total of 192 growing rabbits (96 in each trial) were weaned at 35 d and assigned to 2 different feeding treatments (continuously fed ad libitum or restricted from 35 until 49 d). In the first trial, feed restriction reduced daily feed intake (94.3 vs. 74.2 g; P<0.001), daily weight gain (43.6 vs. 27.1 g; P<0.001) and impaired feed conversion rate (FCR) (2.28 vs. 2.92, P<0.001) in the first 14 d after weaning. Later on, no feed restriction was applied and a compensatory growth was observed in previously restricted rabbits (44.8 vs. 54.8 g/d; P<0.001). Early restricted rabbits did not reach the Spanish commercial weight (2 kg) at 63 d of age and weighed less than full-fed rabbits (1989 vs. 1888 g; P=0.001). Moreover, feed restriction did not improve FCR in the whole fattening period (2.56 on average). The second trial was extended until 70 d to permit restricted rabbits to attain market weight. However, at that age, live weight of restricted rabbits was also lower than that of rabbits always fed ad libitum (2285 vs. 2101 g; P=0.001). In the first trial, no health problem was recorded (average mortality 1.04%) whereas in the second trial feed restriction allowed both mortality (25.6 vs. 6.34%, P=0.017) and morbidity (41.4 vs. 12.7%, P=0.004) to decrease. The higher number of losses in the second trial made economic FCR differ from scientific FCR (3.63 vs. 2.89, on average) in the 35¿70 d period. Moreover, morbidity increased heterogeneity of fattening performance. In conclusion, the interest of feed restriction in Spanish fattening rabbit farms is mitigated by the conventional market weight. Nevertheless, in a context with high rates of digestive troubles, a time-limited access to the feeder enhances health status on the farm and could justify the short delay necessary to reach slaughter weight.Romero, C.; Cuesta, S.; Astillero, J.; Nicodemus, N.; Blas, CD. (2010). Effect of early feed restriction on performance and health status in growing rabbits slaughtered at 2 kg live-weight. World Rabbit Science. 18(4):211-218. doi:10.4995/wrs.2010.77821121818

Efficient and scalable starvation prevention mechanism for token coherence

[EN] Token Coherence is a cache coherence protocol that simultaneously captures the best attributes of the traditional approximations to coherence: direct communication between processors (like snooping-based protocols) and no reliance on bus-like interconnects (like directory-based protocols). This is possible thanks to a class of unordered requests that usually succeed in resolving the cache misses. The problem of the unordered requests is that they can cause protocol races, which prevent some misses from being resolved. To eliminate races and ensure the completion of the unresolved misses, Token Coherence uses a starvation prevention mechanism named persistent requests. This mechanism is extremely inefficient and, besides, it endangers the scalability of Token Coherence since it requires storage structures (at each node) whose size grows proportionally to the system size. While multiprocessors continue including an increasingly number of nodes, both the performance and scalability of cache coherence protocols will continue to be key aspects. In this work, we propose an alternative starvation prevention mechanism, named priority requests, that outperforms the persistent request one. This mechanism is able to reduce the application runtime more than 20 percent (on average) in a 64-processor system. Furthermore, thanks to the flexibility shown by priority requests, it is possible to drastically minimize its storage requirements, thereby improving the whole scalability of Token Coherence. Although this is achieved at the expense of a slight performance degradation, priority requests still outperform persistent requests significantly.This work was partially supported by the Spanish MEC and MICINN, as well as European Commission FEDER funds, under Grants CSD2006-00046 and TIN2009-14475-C04-01. Antonio Robles is taking a sabbatical granted by the Universidad Politecnica de Valencia for updating his teaching and research activities.Cuesta Sáez, BA.; Robles Martínez, A.; Duato Marín, JF. (2011). Efficient and scalable starvation prevention mechanism for token coherence. IEEE Transactions on Parallel and Distributed Systems. 22(10):1610-1623. doi:10.1109/TPDS.2011.30S16101623221

Increasing the effectiveness of directory caches by avoiding the tracking of noncoherent memory blocks

© 2013 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.A key aspect in the design of efficient multiprocessor systems is the cache coherence protocol. Although directory-based protocols constitute the most scalable approach, the limited size of the directory caches together with the growing size of systems may cause frequent evictions and, consequently, the invalidation of cached blocks, which jeopardizes system performance. Directory caches keep track of every memory block stored in processor caches in order to provide coherent access to the shared memory. However, a significant fraction of the cached memory blocks do not require coherence maintenance (even in parallel applications) because they are either accessed by just one processor or they are never modified. In this paper, we propose to deactivate the coherence protocol for those blocks that do not require coherence. This deactivation means directory caches do not have to keep track of noncoherent blocks, which reduces directory cache occupancy and increases its effectiveness. Since the detection of noncoherent blocks is carried out by the operating system, our proposal only requires minor hardware modifications. Simulation results show that, thanks to our proposal, directory caches can avoid the tracking of about 66 percent (on average) of the blocks accessed by a wide range of applications, thereby improving the efficiency of directory caches. This contributes either to shortening the runtime of parallel applications by 15 percent (on average) while keeping directory cache size or to maintaining performance while using directory caches 16 times smaller.This work was supported by the Spanish MICINN, Consolider Programme and Plan E funds, as well as European Commission FEDER funds, under Grants CSD2006-00046 and TIN2009-14475-C04-01. It was also partly supported by (PROMETEO from Generalitat Valenciana (GVA) under Grant ROMETEO/2008/060). B. Cuesta was with Universitat Politecnica de Valencia while working on this paper.Cuesta Sáez, BA.; Ros Bardisa, A.; Gómez Requena, ME.; Robles Martínez, A.; Duato Marín, JF. (2013). Increasing the effectiveness of directory caches by avoiding the tracking of noncoherent memory blocks. IEEE Transactions on Computers. 62(3):482-495. https://doi.org/10.1109/TC.2011.241S48249562

Temporal-Aware Mechanism to Detect Private Data in Chip Multiprocessors

© 2013 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Most of the data referenced by sequential and parallel applications running in current chip multiprocessors are referenced by only one thread and can be considered as private data. A lot of recent proposals leverage this observation to improve many aspects of chip multiprocessors, such as reducing coherence overhead or the access latency to distributed caches. The effectiveness of those proposals depend to a large extent on the amount of detected private data. However, the mechanisms proposed so far do not consider thread migration and the private use of data within different application phases. As a result, a considerable amount of data is not detected as private. In order to make this detection more accurate and reaching more significant improvements, we propose a mechanism that is able to account for both thread migration and private data within application phases. Simulation results for 16-core systems show that, thanks to our mechanism, the average number of pages detected as private significantly increases from 43% in previous proposals up to 74% in ours. Finally, when our detection mechanism is used to deactivate the coherence for private data in a directory protocol, our proposal improves execution time by 13% with respect to previous proposals.This work was supported by the Spanish MINECO, as well as European Commission FEDER funds, under grant TIN2012-38341-C04-01/03 and by the VIRTICAL project (grant agreement no 288574) which is funded by the European Commission within the Research Programme FP7.Ros Bardisa, A.; Cuesta Sáez, BA.; Gómez Requena, ME.; Robles Martínez, A.; Duato Marín, JF. (2013). Temporal-Aware Mechanism to Detect Private Data in Chip Multiprocessors. En Proceedings of the International Conference on Parallel Processing. IEEE. 562-571. https://doi.org/10.1109/ICPP.2013.70S56257

A multiple dating-method approach applied to the Sanabria Lake moraine complex (NW Iberian Peninsula, SW Europe)

New evidence in the NW region of the Iberian Peninsula (c. 42º N 6 ºW) of a glacial advance coeval with the global Last Glacial Maximum (LGM) of the Marine Isotope Stage 2 has been identified through a dataset of exposure ages based on 23 10Be concentration measurements carried out on boulder samples taken from a set of latero-frontal moraines. Results span the interval 19.2e15.4 10Be ka, matching the last deglaciation period when Iberia experienced the coldest and driest conditions of the last 25 ka, and are consistent with Lateglacial chronologies established in other mountain regions from SW Europe. The extent of the LGM stade identified in this work is similar to the local maximum ice extent stade recorded and dated as prior to 33 ka using radiocarbon and optically stimulated luminescence. This work showcases how multiple-dating approaches and detailed geomorphological mapping are required to reconstruct realistic palaeoglacier evolution models

Utilidad de una estrategia de cribado de hipertensión ocular y glaucoma en atención primaria

ObjetivosEvaluar la utilidad de una estrategia de cribado de glaucoma e hipertensión ocular (HTO) medida como número de casos detectados. Evaluar la aceptabilidad de la toma de presión intraocular (PIO) y la aparición de efectos secundarios.DiseñoEstudio descriptivo transversal.EmplazamientoCentro de salud urbano y consulta de oftalmología del hospital de referencia.ParticipantesEn total, 2.044 pacientes mayores de 40 años, seleccionados por muestreo consecutivo entre los que consultaron en el centro de salud durante 9 meses. Se excluyeron los sujetos diagnosticados de glaucoma, HTO, conjuntivitis o enfermedad corneal.IntervencionesToma de PIO con Tonopen XL en atención primaria. Se remitió a oftalmología a los sujetos con una PIO≥21 mmHg. En éstos se midió la PIO con la prueba de Goldmann y, en los que se confirmó la HTO, se realizaron una oftalmoscopia y una campimetría.Mediciones principalesPorcentaje de sujetos con glaucoma, sospecha de glaucoma e HTO confirmada en oftalmología. Valor predictivo positivo (VPP) para HTO.ResultadosSe detectaron 100 sujetos con HTO (4,89%; intervalo de confianza [IC] del 95%, 3,93-5,85%), de los que 21 fueron diagnosticados de glaucoma (1,04%; IC del 95%, 0,57-1,49%) y 10 de sospecha de glaucoma (0,49%; IC del 95%, 0,16-0,82). El VPP para HTO fue del 44,27%. La aceptabilidad de la prueba fue del 98,09%. Ningún paciente presentó efectos secundarios tras la toma de la PIO.ConclusionesLa estrategia evaluada es útil en cuanto al porcentaje de sujetos con glaucoma e HTO detectados. La aceptabilidad de la toma de la PIO con Tonopen XL es alta.ObjectivesTo evaluate the usefulness of a glaucoma and intraocular hypertension screening strategy for new cases detected. To evaluate the acceptability of taking intraocular pressure (IOP) and the appearance of side effects.DesignCross-sectional, descriptive study.SettingAn urban health centre and the ophthalmology clinic of its main hospital.ParticipantsA total of 2044 patients aged over 40, 63.5% women and 36.5% men, with a mean age of 61.23 (SD, 11.42). They were selected by consecutive sampling from patients who visited the health centre over a 9-month period. Subjects diagnosed with glaucoma, ocular hypertension (OH), conjunctivitis, or corneal pathology were excluded.InterventionsTaking of IOP with Tonopen XL in primary care. Subjects with IOP ≥21 mm Hg were referred to ophthalmology. In these patients, IOP was measured with Goldmann, and patients with confirmed OH received ophthalmoscopy and campimetry.Main measurementsPercentage of subjects with glaucoma, suspected glaucoma, and OH confirmed in ophthalmology. Positive predictive value (PPV) for OH.ResultsOne hundred subjects with OH were detected (4.89%; 95% CI, 3.93%-5.85%), of whom 21 were diagnosed with glaucoma (1.04%; 95% CI, 0.57-1.49) and 10 with suspected glaucoma (0.49%; 95% CI, 0.16-0.82). The PPV for OH was 44.27%. The acceptability of the test was 98.09%. No patients presented with side-effects following the taking of their IOP.ConclusionsThe strategy evaluated is useful in terms of the number of subjects with glaucoma and OH detected. The acceptability of taking IOP with Tonopen XL was high