This thesis proposes to reduce the latency of MPI receive operations on cacheless architectures, by removing the delay of copying messages when they are first received. This is achieved by copying the messages directly into buffers in the lowest level of the memory hierarchy (e.g., scratchpad memory). The previously proposed solution introduced an Indirection Cache which would map between the receive variables and the buffered message payload locations. This proved somewhat beneficial, but the lookup penalty of the Indirection Cache limited its effectiveness. Therefore this thesis proposes that a most recently used buffer (i.e., an Indirection Buffer) be placed in front of the Indirection Cache to eliminate this penalty and speed up access. The tests conducted demonstrated that this method was indeed effective and improved over the original method by at least an order of magnitude. Finally, examination of implementation feasibility showed that this could be implemented with a small Cache, and that even with access times 6x slower than initially assumed, the approach with the Indirection Buffer would still be effective. / Graduate

<p>We present an indirection architecture for the Internet called SelNet. SelNet provides a uniform indirection mechanism for controlling the route that packets take through the network and which functions are invoked to process these packets. In the current Internet, at least for the majority of users, there is only one way that a packet can go and that is to the default route. Whilst this is sufficient for many applications, numerous applications have arisen which require alternative routes or processing to be present not only at the application-layer of the protocol stack, but at the network-layer itself. Solutions to such scenarios attempt to place an indirection point between the communicating end-systems either with a middlebox (such as a proxy) or by altering one or more of the Internet's naming systems. However these approaches lead to an application-specific network, which is against the Internet's design goals. We argue for a uniform approach to indirection instead of building multiple, partially overlapping structures as is the current trend. SelNet differs from existing indirection approaches in that it is function-orientated, rather than node-orientated and that it provides an explicit, controllable resolution mechanism for resolving host names and services. The motivation behind our approach is to create efficient indirection structures for supporting new applications which have indirection requirements. We present a detailed design and specification of SelNet. We then go on to describe implementation work with the LUNAR ad-hoc routing protocol and the Janus middleware for accessing sensor networks systems. The purpose of this implementation work is to demonstrate the feasibility of SelNet and its ability to reach its goals.</p>

We present an indirection architecture for the Internet called SelNet. SelNet provides a uniform indirection mechanism for controlling the route that packets take through the network and which functions are invoked to process these packets. In the current Internet, at least for the majority of users, there is only one way that a packet can go and that is to the default route. Whilst this is sufficient for many applications, numerous applications have arisen which require alternative routes or processing to be present not only at the application-layer of the protocol stack, but at the network-layer itself. Solutions to such scenarios attempt to place an indirection point between the communicating end-systems either with a middlebox (such as a proxy) or by altering one or more of the Internet's naming systems. However these approaches lead to an application-specific network, which is against the Internet's design goals. We argue for a uniform approach to indirection instead of building multiple, partially overlapping structures as is the current trend. SelNet differs from existing indirection approaches in that it is function-orientated, rather than node-orientated and that it provides an explicit, controllable resolution mechanism for resolving host names and services. The motivation behind our approach is to create efficient indirection structures for supporting new applications which have indirection requirements. We present a detailed design and specification of SelNet. We then go on to describe implementation work with the LUNAR ad-hoc routing protocol and the Janus middleware for accessing sensor networks systems. The purpose of this implementation work is to demonstrate the feasibility of SelNet and its ability to reach its goals.

<div>Remote Direct Memory Access, or RDMA, is a technology that allows one computer server to direct access the memory of another server without involving its CPU. Compared with traditional network technologies, RDMA offers several benefits including low latency, high throughput, and low CPU utilization. These features are especially attractive to datacenters, and because of this, datacenters have started to adopt RDMA in production scale in recent years.</div><div>However, RDMA was designed for confined, single-tenant, High-Performance-Computing (HPC) environments. Many of its design choices do not fit datacenters well, and it cannot be readily used by datacenter applications. To use RDMA, current datacenter applications have to build customized software stacks and fine-tune their performance. In addition, RDMA offers limited scalability and does not have good support for resource sharing or protection across different applications.</div><div>This dissertation sets out to seek solutions that can solve issues of RDMA in a systematic way and makes it more suitable for a wide range of datacenter applications.</div><div>Our first task is to make RDMA more scalable, easier to use, and have better support for safe resource sharing in datacenters. For this purpose, we propose to add an indirection layer on top of native RDMA to virtualize its low-level abstraction into a high-level one. This indirection layer safely manages RDMA resources for different datacenter applications and also provide a means for better scalability.</div><div>After making RDMA more suitable for datacenter environments, our next task is to build applications that can exploit all the benefits from (our improved) RDMA. We designed a set of systems that store data in remote persistent memory and let client machines access these data through pure one-sided RDMA communication. These systems lower monetary and energy cost compared to traditional datacenter data stores (because no processor is needed at remote persistent memory), while achieving good performance and reliability.</div><div>Our final task focuses on a completely different and so far largely overlooked one — security implications of RDMA. We discovered several key vulnerabilities in the one-sided communication pattern and in RDMA hardware. We exploited one of them to create a novel set of remote side-channel attacks, which we are able to launch on a widely used RDMA system with real RDMA hardware.</div><div>This dissertation is one of the initial efforts in making RDMA more suitable for datacenter environments from scalability, usability, cost, and security aspects. We hope that the systems we built as well as the lessons we learned can be helpful to future networking and systems researchers and practitioners.</div>

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La nueva tendencia para aumentar el rendimiento de los futuroscomputadores son los multiprocesadores en un solo chip (CMPs). Seespera que en un futuro cercano salgan al mercado CMPs con decenas deprocesadores. Hoy en d�a, la mejor manera de mantener la coherencia decache en estos sistemas es mediante los protocolos basados endirectorio. Sin embargo, estos protocolos tienen dos grandesproblemas: una gran sobrecarga de memoria y una alta latencia de losfallos de cache.Esta tesis se ha centrado en estos problemas claves para la eficienciay escalabilidad del CMP. En primer lugar, se ha presentado unaorganizaci�n de directorios escalable. En segundo lugar, se hanpropuesto los protocolos de coherencia directa, que evitan laindirecci�n al nodo home y, por tanto, reducen el tiempo de ejecuci�nde las aplicaciones. Por �ltimo, se ha desarrollado una pol�tica demapeo para caches compartidas pero f�sicamente distribuidas, quereduce la latencia de acceso y garantiza una distribuci�n uniforme delos datos con el fin de reducir su tasa de fallos. Esto se traducefinalmente en un menor tiempo de ejecuci�n para las aplicaciones. / Chip multiprocessors (CMPs) constitute the new trend for increasingthe performance of future computers. In the near future, chips withtens of cores will become more popular. Nowadays, directory-basedprotocols constitute the best alternative to keep cache coherence inlarge-scale systems. Nevertheless, directory-based protocols have twoimportant issues that prevent them from achieving better scalability:the directory memory overhead and the long cache miss latencies.This thesis focuses on these key issues. The first proposal is ascalable distributed directory organization that copes with the memoryoverhead of directory-based protocols. The second proposal presentsthe direct coherence protocols, which are aimed at avoiding theindirection problem of traditional directory-based protocols and,therefore, they improve applications' performance. Finally, a novelmapping policy for distributed caches is presented. This policyreduces the long access latency while lessening the number of off-chipaccesses, leading to improvements in applications' execution time.