18 research outputs found
Page size aware cache prefetching
The increase in working set sizes of contemporary applications outpaces the growth in cache sizes, resulting in frequent main memory accesses that deteriorate system per- formance due to the disparity between processor and memory speeds. Prefetching data blocks into the cache hierarchy ahead of demand accesses has proven successful at attenuating this bottleneck. However, spatial cache prefetchers operating in the physical address space leave significant performance on the table by limiting their pattern detection within 4KB physical page boundaries when modern systems use page sizes larger than 4KB to mitigate the address translation overheads. This paper exploits the high usage of large pages in modern systems to increase the effectiveness of spatial cache prefetch- ing. We design and propose the Page-size Propagation Module (PPM), a ”architectural scheme that propagates the page size information to the lower-level cache prefetchers, enabling safe prefetching beyond 4KB physical page boundaries when the accessed blocks reside in large pages, at the cost of augmenting the first-level cachesâ Miss Status Holding Register (MSHR) entries with one additional bit. PPM is compatible with any cache prefetcher without implying design modifications. We capitalize on PPMâs benefits by designing a module that consists of two page size aware prefetchers that inherently use different page sizes to drive prefetching. The composite module uses adaptive logic to dynamically enable the most appropriate page size aware prefetcher. Finally, we show that the proposed designs are transparent to which cache prefetcher is used. We apply the proposed page size exploitation techniques to four state-of-the-art spatial cache prefetchers. Our evalua- tion shows that our proposals improve single-core geomean performance by up to 8.1% (2.1% at minimum) over the original implementation of the considered prefetchers, across 80 memory-intensive workloads. In multi-core contexts, we report geomean speedups up to 7.7% across different cache prefetchers and core configurations.This work is supported by the Spanish Ministry of Science and Technology through the PID2019-107255GB project, the Generalitat de Catalunya (contract 2017-SGR-1414), the European Union Horizon 2020 research and innovation program under grant agreement No 955606 (DEEP-SEA EU project), the National Science Foundation through grants CNS-1938064 and CCF-1912617, and the Semiconductor Research Corporation project GRC 2936.001. Georgios Vavouliotis has been supported by the Spanish Ministry of Economy, Industry, and Competitiveness and the European Social Fund under the FPI fellowship No. PRE2018-087046. Marc Casas has been partially supported by the Grant RYC2017-23269 funded by MCIN/AEI/10.13039/501100011033 and ESF âInvesting in your futureâ.Peer ReviewedPostprint (author's final draft
Active strategies for coordination of solitary robots
Thesis (PhD)--Stellenbosch University, 2020.ENGLISH ABSTRACT: This thesis considers the problem of search of an unknown environment
by multiple solitary robots: self-interested robots without prior knowledge
about each other, and with restricted perception and communication capacity.
When solitary robots accidentally interact with each other, they can
leverage each otherâs information to work more effectively. In this thesis,
we consider three problems related to the treatment of solitary robots: coordination,
construction of a view of the network formed when robots interact,
and classifier fusion. Coordination is the key focus for search and
rescue. The other two problems are related areas inspired by the problems
we encountered while developing our coordination method. We propose
a coordination strategy based on cellular decomposition of the search environment,
which provides sustainable performance when a known available
search time (bound) is insufficient to cover the entire search environment.
A sustainable performance is achieved when robots that know about
each other explore non-overlapping regions. For network construction, we
propose modifications to a scalable decentralised method for constructing
a model of network topology which reduces the number of messages exchanged
between interacting nodes. The method has wider potential application
than mobile robotics. For classifier fusion, we propose an iterative method where outputs of classifiers are combined without using any further
information about the behaviour of the individual classifiers. Our approaches
for each of these problems are compared to state-of-the-art methods.AFRIKAANSE OPSOMMING: Hierdie tesis beskou die probleem van soektog in ân onbekende omgewing
deur ân aantal alleenstaande robotte: selfbelangstellende robotte sonder voorafgaande
kennis van mekaar, en met beperkte persepsie- en kommunikasievermoëns.
Wanneer alleenstaande robotte toevallig mekaar raakloop, kan
hulle met mekaar inligting uitruil om meer effektief te werk. Hierdie tesis
beskou drie probleme wat verband hou met die hantering van alleenstaande
robotte: konstruksie van ân blik van die netwerk gevorm deur interaksie
tussen robotte, koördinasie en klassifiseerdersamesmelting. Koördinasie
is die hoof fokuspunt vir soek en redding. Die ander twee probleme
is uit verwante areas, gemotiveer deur uitdagings wat ons ervaar het tydens
die ontwikkeling van ons koördineringsmetode. Ons stel ân skaleerbare desentraliseerde
metode voor om ân model van netwerktopologie te bou wat
minder boodskappe tussen wisselwerkende nodusse hoet te verruil. Die
metode het wyer potensiële toepassings as mobiele robotika. Vir koördinasie,
stel ons ân strategie voor gebaseer op sellulĂȘre ontbinding van die
soekomgewing, wat volhoubare prestasie toon wanneer ân bekende soektyd
onvoldoende is om die hele soekomgewing te dek. Vir klassifiseerdersamesmelting,
stel ons ân iteratiewe metode voor, waar klassifiseerders se voorspellings gekombineer word sonder om enige verdere inligting oor die
gedrag van die individuele klassifiseerders te gebruik. Ons benaderings vir
elkeen van hierdie probleme word vergelyk met stand-van-die-kuns metodes.The financial assistance of the African Institute for Mathematical Sciences (AIMS) and CSIR-SU Centre
for Artificial Intelligence Research Group (CSIR-SU CAIR) towards this research is hereby acknowledged.
Opinions expressed and conclusions arrived at, are those of the author and are not necessarily
to be attributed to the AIMS and CSIR-SU CAIR.Doctora
Measuring the impact of COVID-19 on hospital care pathways
Care pathways in hospitals around the world reported significant disruption during the recent COVID-19 pandemic but measuring the actual impact is more problematic. Process mining can be useful for hospital management to measure the conformance of real-life care to what might be considered normal operations. In this study, we aim to demonstrate that process mining can be used to investigate process changes associated with complex disruptive events. We studied perturbations to accident and emergency (A &E) and maternity pathways in a UK public hospital during the COVID-19 pandemic. Co-incidentally the hospital had implemented a Command Centre approach for patient-flow management affording an opportunity to study both the planned improvement and the disruption due to the pandemic. Our study proposes and demonstrates a method for measuring and investigating the impact of such planned and unplanned disruptions affecting hospital care pathways. We found that during the pandemic, both A &E and maternity pathways had measurable reductions in the mean length of stay and a measurable drop in the percentage of pathways conforming to normative models. There were no distinctive patterns of monthly mean values of length of stay nor conformance throughout the phases of the installation of the hospitalâs new Command Centre approach. Due to a deficit in the available A &E data, the findings for A &E pathways could not be interpreted