Energy Aware Runtime Systems for Elastic Stream Processing Platforms

Following an invariant growth in the required computational performance of processors, the multicore revolution started around 20 years ago. This revolution was mainly an answer to power dissipation constraints restricting the increase of clock frequency in single-core processors. The multicore revolution not only brought in the challenge of parallel programming, i.e. being able to develop software exploiting the entire capabilities of manycore architectures, but also the challenge of programming heterogeneous platforms. The question of “on which processing element to map a specific computational unit?”, is well known in the embedded community. With the introduction of general-purpose graphics processing units (GPGPUs), digital signal processors (DSPs) along with many-core processors on different system-on-chip platforms, heterogeneous parallel platforms are nowadays widespread over several domains, from consumer devices to media processing platforms for telecom operators. Finding mapping together with a suitable hardware architecture is a process called design-space exploration. This process is very challenging in heterogeneous many-core architectures, which promise to offer benefits in terms of energy efficiency. The main problem is the exponential explosion of space exploration. With the recent trend of increasing levels of heterogeneity in the chip, selecting the parameters to take into account when mapping software to hardware is still an open research topic in the embedded area. For example, the current Linux scheduler has poor performance when mapping tasks to computing elements available in hardware. The only metric considered is CPU workload, which as was shown in recent work does not match true performance demands from the applications. Doing so may produce an incorrect allocation of resources, resulting in a waste of energy. The origin of this research work comes from the observation that these approaches do not provide full support for the dynamic behavior of stream processing applications, especially if these behaviors are established only at runtime. This research will contribute to the general goal of developing energy-efficient solutions to design streaming applications on heterogeneous and parallel hardware platforms. Streaming applications are nowadays widely spread in the software domain. Their distinctive characiteristic is the retrieving of multiple streams of data and the need to process them in real time. The proposed work will develop new approaches to address the challenging problem of efficient runtime coordination of dynamic applications, focusing on energy and performance management.Efter en oföränderlig tillväxt i prestandakrav hos processorer, började den flerkärniga processor-revolutionen för ungefär 20 år sedan. Denna revolution skedde till största del som en lösning till begränsningar i energieffekten allt eftersom klockfrekvensen kontinuerligt höjdes i en-kärniga processorer. Den flerkärniga processor-revolutionen medförde inte enbart utmaningen gällande parallellprogrammering, m.a.o. förmågan att utveckla mjukvara som använder sig av alla delelement i de flerkärniga processorerna, men också utmaningen med programmering av heterogena plattformar. Frågeställningen ”på vilken processorelement skall en viss beräkning utföras?” är väl känt inom ramen för inbyggda datorsystem. Efter introduktionen av grafikprocessorer för allmänna beräkningar (GPGPU), signalprocesserings-processorer (DSP) samt flerkärniga processorer på olika system-on-chip plattformar, är heterogena parallella plattformar idag omfattande inom många domäner, från konsumtionsartiklar till mediaprocesseringsplattformar för telekommunikationsoperatörer. Processen att placera beräkningarna på en passande hårdvaruplattform kallas för utforskning av en designrymd (design-space exploration). Denna process är mycket utmanande för heterogena flerkärniga arkitekturer, och kan medföra fördelar när det gäller energieffektivitet. Det största problemet är att de olika valmöjligheterna i designrymden kan växa exponentiellt. Enligt den nuvarande trenden som förespår ökad heterogeniska aspekter i processorerna är utmaningen att hitta den mest passande placeringen av beräkningarna på hårdvaran ännu en forskningsfråga inom ramen för inbyggda datorsystem. Till exempel, den nuvarande schemaläggaren i Linux operativsystemet är inkapabel att hitta en effektiv placering av beräkningarna på den underliggande hårdvaran. Det enda mätsättet som används är processorns belastning vilket, som visats i tidigare forskning, inte motsvarar den verkliga prestandan i applikationen. Användning av detta mätsätt vid resursallokering resulterar i slöseri med energi. Denna forskning härstammar från observationerna att dessa tillvägagångssätt inte stöder det dynamiska beteendet hos ström-processeringsapplikationer (stream processing applications), speciellt om beteendena bara etableras vid körtid. Denna forskning kontribuerar till det allmänna målet att utveckla energieffektiva lösningar för ström-applikationer (streaming applications) på heterogena flerkärniga hårdvaruplattformar. Ström-applikationer är numera mycket vanliga i mjukvarudomän. Deras distinkta karaktär är inläsning av flertalet dataströmmar, och behov av att processera dem i realtid. Arbetet i denna forskning understöder utvecklingen av nya sätt för att lösa det utmanade problemet att effektivt koordinera dynamiska applikationer i realtid och fokus på energi- och prestandahantering

The interaction network : a performance measurement and evaluation tool for loosely-coupled distributed systems

Much of today's computing is done on loosely-coupled distributed systems. Performance issues for such systems usually involve interactive performance, that is, system responsiveness as perceived by the user. The goal of the work described in this thesis has been to develop and implement tools and techniques for the measurement and evaluation of interactive performance in loosely-coupled distributed systems. The author has developed the concept of the interaction network, an acyclic directed graph designed to represent the processing performed by a distributed system in response to a user input. The definition of an interaction network is based on a general model of a loosely-coupled distributed system and a general model of user interactions. The author shows that his distributed system model is a valid abstraction for a wide range of present-day systems. Performance monitors for traditional time-sharing systems reported performance information, such as overall resource utilisations and queue lengths, for the system as a whole. Performance problems are now much more difficult, because systems are much more complex. Recent monitors designed specifically for distributed systems have tended to present performance information for execution of a distributed program, for example the time spent in each of a program's procedures. In the work described in this thesis, performance information is reported for one or more user interactions, where a user interaction is defined to be a single user input and all of the processing performed by the system on receiving that input. A user interaction is seen as quite different from a program execution; a user interaction includes the partial or total execution of one or more programs, and a program execution performs work as part of one or more user interactions. Several methods are then developed to show how performance information can be obtained from analysis of interaction networks. One valuable type of performance information is a decomposition of response time into times spent in each of some set of states, where each state might be defined in terms of the hardware and software resources used. Other performance information can be found from displays of interaction networks. The critical path through an interaction network is then defined as showing the set of activities such that at least one must be reduced in length if the response time of the interaction is to be reduced; the critical path is used in both response time decompositions and in displays of interaction networks. It was thought essential to demonstrate that interaction networks could be recorded for a working operating system. INMON, a prototype monitor based on the interaction network concept, has been constructed to operate in the SunOS environment. INMON consists of data collection and data analysis components. The data collection component, for example, involved the adding of 53 probes to the SunOS operating system kernel. To record interaction networks, a high-resolution global timebase is needed. A clock synchronisation program has been written to provide INMON with such a timebase. It is suggested that the method incorporates a number of improvements over other clock synchronisation methods. Several experiments have been performed to show that INMON can produce very detailed performance information for both individual user interactions and groups of user interactions, with user input being made through either character-based or graphical interfaces. The main conclusion reached in this thesis is that representing the processing component of a user interaction in an interaction network is a very valuable way of approaching the problem of measuring interactive performance in a loosely-coupled distributed system. An interaction network contains a very detailed record of the execution of an interaction and, from this record, a great deal of performance (and other) information can be derived. Construction of INMON has demonstrated that interaction networks can be identified, recorded, and analysed