Designing energy-efficient computing systems using equalization and machine learning

As technology scaling slows down in the nanometer CMOS regime and mobile computing becomes more ubiquitous, designing energy-efficient hardware for mobile systems is becoming increasingly critical and challenging. Although various approaches like near-threshold computing (NTC), aggressive voltage scaling with shadow latches, etc. have been proposed to get the most out of limited battery life, there is still no “silver bullet” to increasing power-performance demands of the mobile systems. Moreover, given that a mobile system could operate in a variety of environmental conditions, like different temperatures, have varying performance requirements, etc., there is a growing need for designing tunable/reconfigurable systems in order to achieve energy-efficient operation. In this work we propose to address the energy- efficiency problem of mobile systems using two different approaches: circuit tunability and distributed adaptive algorithms. Inspired by the communication systems, we developed feedback equalization based digital logic that changes the threshold of its gates based on the input pattern. We showed that feedback equalization in static complementary CMOS logic enabled up to 20% reduction in energy dissipation while maintaining the performance metrics. We also achieved 30% reduction in energy dissipation for pass-transistor digital logic (PTL) with equalization while maintaining performance. In addition, we proposed a mechanism that leverages feedback equalization techniques to achieve near optimal operation of static complementary CMOS logic blocks over the entire voltage range from near threshold supply voltage to nominal supply voltage. Using energy-delay product (EDP) as a metric we analyzed the use of the feedback equalizer as part of various sequential computational blocks. Our analysis shows that for near-threshold voltage operation, when equalization was used, we can improve the operating frequency by up to 30%, while the energy increase was less than 15%, with an overall EDP reduction of ≈10%. We also observe an EDP reduction of close to 5% across entire above-threshold voltage range. On the distributed adaptive algorithm front, we explored energy-efficient hardware implementation of machine learning algorithms. We proposed an adaptive classifier that leverages the wide variability in data complexity to enable energy-efficient data classification operations for mobile systems. Our approach takes advantage of varying classification hardness across data to dynamically allocate resources and improve energy efficiency. On average, our adaptive classifier is ≈100× more energy efficient but has ≈1% higher error rate than a complex radial basis function classifier and is ≈10× less energy efficient but has ≈40% lower error rate than a simple linear classifier across a wide range of classification data sets. We also developed a field of groves (FoG) implementation of random forests (RF) that achieves an accuracy comparable to Convolutional Neural Networks (CNN) and Support Vector Machines (SVM) under tight energy budgets. The FoG architecture takes advantage of the fact that in random forests a small portion of the weak classifiers (decision trees) might be sufficient to achieve high statistical performance. By dividing the random forest into smaller forests (Groves), and conditionally executing the rest of the forest, FoG is able to achieve much higher energy efficiency levels for comparable error rates. We also take advantage of the distributed nature of the FoG to achieve high level of parallelism. Our evaluation shows that at maximum achievable accuracies FoG consumes ≈1.48×, ≈24×, ≈2.5×, and ≈34.7× lower energy per classification compared to conventional RF, SVM-RBF , Multi-Layer Perceptron Network (MLP), and CNN, respectively. FoG is 6.5× less energy efficient than SVM-LR, but achieves 18% higher accuracy on average across all considered datasets

Designing energy-efficient sub-threshold logic circuits using equalization and non-volatile memory circuits using memristors

The very large scale integration (VLSI) community has utilized aggressive complementary metal-oxide semiconductor (CMOS) technology scaling to meet the ever-increasing performance requirements of computing systems. However, as we enter the nanoscale regime, the prevalent process variation effects degrade the CMOS device reliability. Hence, it is increasingly essential to explore emerging technologies which are compatible with the conventional CMOS process for designing highly-dense memory/logic circuits. Memristor technology is being explored as a potential candidate in designing non-volatile memory arrays and logic circuits with high density, low latency and small energy consumption. In this thesis, we present the detailed functionality of multi-bit 1-Transistor 1-memRistor (1T1R) cell-based memory arrays. We present the performance and energy models for an individual 1T1R memory cell and the memory array as a whole. We have considered TiO2- and HfOx-based memristors, and for these technologies there is a sub-10% difference between energy and performance computed using our models and HSPICE simulations. Using a performance-driven design approach, the energy-optimized TiO2-based RRAM array consumes the least write energy (4.06 pJ/bit) and read energy (188 fJ/bit) when storing 3 bits/cell for 100 nsec write and 1 nsec read access times. Similarly, HfOx-based RRAM array consumes the least write energy (365 fJ/bit) and read energy (173 fJ/bit) when storing 3 bits/cell for 1 nsec write and 200 nsec read access times. On the logic side, we investigate the use of equalization techniques to improve the energy efficiency of digital sequential logic circuits in sub-threshold regime. We first propose the use of a variable threshold feedback equalizer circuit with combinational logic blocks to mitigate the timing errors in digital logic designed in sub-threshold regime. This mitigation of timing errors can be leveraged to reduce the dominant leakage energy by scaling supply voltage or decreasing the propagation delay. At the fixed supply voltage, we can decrease the propagation delay of the critical path in a combinational logic block using equalizer circuits and, correspondingly decrease the leakage energy consumption. For a 8-bit carry lookahead adder designed in UMC 130 nm process, the operating frequency can be increased by 22.87% (on average), while reducing the leakage energy by 22.6% (on average) in the sub-threshold regime. Overall, the feedback equalization technique provides up to 35.4% lower energy-delay product compared to the conventional non-equalized logic. We also propose a tunable adaptive feedback equalizer circuit that can be used with sequential digital logic to mitigate the process variation effects and reduce the dominant leakage energy component in sub-threshold digital logic circuits. For a 64-bit adder designed in 130 nm our proposed approach can reduce the normalized delay variation of the critical path delay from 16.1% to 11.4% while reducing the energy-delay product by 25.83% at minimum energy supply voltage. In addition, we present detailed energy-performance models of the adaptive feedback equalizer circuit. This work serves as a foundation for the design of robust, energy-efficient digital logic circuits in sub-threshold regime

Proceedings of the 19th Sound and Music Computing Conference

Proceedings of the 19th Sound and Music Computing Conference - June 5-12, 2022 - Saint-Étienne (France). https://smc22.grame.f

Trust me! Vorschlag zum Umgang mit der Vertrauensfrage im digitalen Zeitalter

Die Arbeit behandelt die Frage, wie in Zeiten umfassender, technologisch beförderter Veränderung, Vertrauen als wirksames Instrument selbstbestimmten Handelns dienen kann. Sie orientiert sich dabei an Luhmanns Begriff rationalen, zur Komplexitätsreduktion dienenden Vertrauens. Sie gliedert sich in zwei Teile. Im ersten Teil wird der digital geprägte Alltag als Grundlage für Vertrauen betrachtet. Dazu wird der Begriff eines „digitalen Systems“ eingeführt. Dieser dient als Erklärungsmodell, das den Systembegriff aus der Systemtheorie aufgreift und darin Merkmale sozialer und technischer Systeme zusammenführt. Es wird argumentiert, dass digitale Kommunikation und der Code, der dieser zugrundeliegt, das sozialen System Gesellschaft zunehmend gestalten und strukturell „ordnen.” Damit wird das Vermögen, Daten zu verarbeiten, und die Verfügungsgewalt über diese Daten zur Voraussetzung für Macht und Teilhabe. Die Freigabe von Daten wird zum digital anschlussfähigen Vertrauenserweis. Inhaltlich fokussiert der erste Teil auf gesellschaftliche Praktiken der Datenerhebung und -verwertung. Es wird aufgezeigt, wie sich Kommunikations- und Kooperationsmechanismen verändern und neue Machtstrukturen mit Tendenz zu einem totalen System entstehen. Ergänzend werden mithilfe soziologischer und historischer Konzepte einige Grundzüge digital determinierter Ordnung herausgearbeitet, und es erfolgt eine Annäherung an deren ideologischen Unterbau. Dieser wird auf die Prämissen ‚Maschinen>Menschen‘ und ‚tertium non datur‘ zurückgeführt. Im zweiten Teil wird untersucht, wie der Einzelne im digitalen Alltag Vertrauen zur Grundlage rationalen und gestaltenden Handelns machen kann. Dazu werden zunächst Vertrauen und Misstrauen als „Mechanismen“ mit bestimmten Funktionen und Kosten betrachtet. Im Anschluss erfolgt, angelehnt an ein Modell von Kelton et al., eine Dekonstruktion des Vertrauensbegriffs und eine Spiegelung vertrauensrelevanter Kriterien an Erkenntnissen aus Wissenschaft und Praxis. Untersucht werden: 1. Vorbedingungen dafür, dass Vertrauen benötigt wird und entstehen kann (Ungewissheit, Abhängigkeit, Verletzbarkeit). Dieser Abschnitt befasst sich mit Machtasymmetrien und Verletzungsmöglichkeiten durch die intransparente Verarbeitung von Daten. 2. Stufen des Vertrauensaufbaus (Gefühlsbindung, Vertrautheit, Eigenkontrolle, Fremdkontrolle und Sinn). Gezeigt wird, wie diese instrumentalisiert werden können und wie insbesondere arational wirkende Mechanismen den Anschein persönlichen Vertrauens und gemeinsamen Sinns befördern können. Betrachtet wird auch die Rolle von Wahrheit, von Erwartungen, Deutungsangeboten und Kommunikationsmustern. Es wird gezeigt, welche Faktoren das Ausüben vertrauensstützender Kontrolle behindern – und wie rationales Vertrauen dennoch gelernt werden kann. 3. Rahmenbedingungen, die das Vertrauen prägen (Selbstvertrauen, das Vertrauen der anderen, Kontext). In diesem Abschnitt wird u.a. beleuchtet, wie technische Voreinstellungen soziale Praktiken befördern und wann einer augenscheinlichen Vertrauensbeziehung keine belastbare Vertrauenspraxis zugrundeliegt. Dies berührt unter anderem die Zuweisung von Risiko und Gefahr. Außerdem werden einige gesetzliche, technische und ökonomische Rahmenbedingungen für rationales Vertrauen aufgeführt. 4. Anzeichen für Vertrauenswürdigkeit (Kompetenz, Berechenbarkeit, Wohlwollen, Rücksichtnahme und Ethik). Es wird argumentiert, dass sich das Vertrauen im digitalen System überwiegend auf einen imaginierten Vertrauenspartner richtet, und mit anderen Vertrauensformen verglichen. In der Auseinandersetzung mit der Praxis fokussiert dieser Abschnitt auf die Möglichkeiten und Grenzen algorithmischer Entscheidungsfindung, unter besonderer Berücksichtigung des Machtanspruchs im Begriff „Ethische KI“. Anhaltspunkte für Ethik werden in einem separaten Kapitel (unter Setzen einer Vertrauensvermutung und Einziehen von „Lernschwellen“ für eventuell notwendiges Misstrauen) weiter vertieft. Es wird aufgezeigt, wie die rationale Auseinandersetzung mit Vertrauen in letzter Instanz auf die Sinnfrage hinführt

Housing quality and lost (public) space in Croatia

IN ENGLISH: In the post-socialist period and within the current social transition context, urban and rural Croatia has, just like other transition countries, experienced many changes in the social structure and space. One example is the housing quality which is a replica of the situation in the Croatian society and has also undergone some major changes. Socially oriented housing construction co-financed by the state and the cities is in an unfavourable position compared to private housing construction. In the last twenty years the amount of the social housing construction has been only a minor part of the total contruction work in the country. For instance, out of nine newly planned residential housing developments in Zagreb, the capital city, only three have been completed and the work on the rest of them has stopped and is unlikely to continue. Private construction work prevails especially on the edge of the city and is characterised by high density housing. This type of housing construction doesn't benefit the majority of citizens in search of accommodation (price per square meter is too high, low-quality building). There is also a big problem of the community facilities (primary and secondary infrastructure, schools, kindergartens, playgrounds, green areas, sidewalks, public transport etc.). The existing globalisation-transition circumstances of the Croatian society corroborate the fact which experts of various profiles often point out: ignoring the process of (urban) planning will irreparably damage the space. The city transformation shows the absence of comprehensive urban planning which results in an ever increasing number of random buildings which do not fit in the surroundings. This leads up to yet another important issue – the shrinking and, in some cases, disappearance of public space which becomes the “lost space“. In recent years there has been a lot of building in the city core and on the edge which does not quite fit in the existing urban structure, image or the skyline of the city. The current situation in the process of planning can be characterized as a conflict and imbalance between the powerful actors (mostly political and economic) and less powerful actors (mostly professional and civil). The actors who have the political power and influence and the ones who possess the capital are forming an “alliance” between two important layers of the social structure. The lack of civil and professional actors, “lost spatial actors”, and therefore of civic aggregation is also present and that is also the cause of public space “disappearance” and undermined process of public participation. --------------- IN CROATIAN: U postsocijalističkom razdoblju i trenutnom tranzicijskom kontekstu urbana i ruralna Hrvatska su, kao i ostale tranzicijske zemlje, doživjele mnoge promjene u društvenoj strukturi i samom prostoru. Na primjeru kvalitete stanovanja kao replike stanja u hrvatskom društvu mogu se vidjeti značajne promjene. Društveno usmjerena stambena izgradnja sufinancirana od strane države i gradova je stoga rjeđa i u nepovoljnijoj je situaciji prema privatnoj stanogradnji. Zadnjih dvadeset godina udjel socijalne stambene gradnje je zanemariv u ukupnoj izgradnji na razini zemlje. Primjerice, od devet planiranih stambenih naselja izgrađenih po modelu POS-a u Zagrebu samo su tri i završena. Na ostalima je proces gradnje zastao i ne čini se da će se privesti kraju. Privatna je gradnje prisutnija, posebno na rubovima grada, a obilježava je visoka gustoća gradnje. Ovakav tip gradnje ne odgovara većini stanovnika koji su u procesu potražnje stambene nekretnine (visoka cijena kvadratnog metra, a slaba kvaliteta gradnje). Postoji također i problem nedostatne opremljenosti susjedstva (primarna i sekundarna infrastruktura, škole, vrtići, igrališta, zelene površine, pješačke staze, javni transport itd.). Navedene globalizacijsko-tranzicijske okolnosti hrvatskog društva potvrđuju ono što eksperti različitih profila ističu, a to je da će ignoriranje procesa (urbanog) planiranja nepovratno uništiti prostor gradova. Ovakve transformacije pokazuju nedostatak sustavnog urbanog planiranja što rezultira sve većim brojem zgrada koje se ne uklapaju u neposrednu okolinu. To nadalje dovodi do drugog važnog aspekta – smanjivanja i u nekim slučajevima, nestanka javnog prostora koji postaje „izgubljeni prostor“. Posljednjih je godina izgrađen velik broj zgrada, i u središtu i na rubovima grada, koje se ne uklapaju u postojeću urbanu strukturu, izgled ili vizuru grada. Ovakvu situaciju obilježavaju sukob i neravnoteža između moćnijih društvenih aktera (većinom političkih i ekonomskih) i onih manje moćnih (većinom profesionalnih i civilnih). Politički i ekonomski akteri se često povezuju u „savez“ dvaju najjačih u društvenoj strukturi. S druge strane nedostatak utjecaja civilnih i profesionalnih aktera kao „izgubljenih prostornih aktera“ dovodi do „nestanka“ javnih prostora te smanjenja važnosti procesa participacije (sudjelovanja javnosti)