Processors emit non-trivial amounts of electromagnetic radiation, creating interference in frequency bands used by wireless communication technologies such as cellular, WiFi and Bluetooth. We introduce the problem of in-band radio frequency noise as a form of electromagnetic interference (EMI) to the computer architecture community as a technical challenge to be addressed. This paper proposes the new idea of Dynamic EMI Shifting (DEMIS) where architectural and/or compiler changes allow the EMI to be shifted at runtime. DEMIS processors dynamically move the interference from bands used during communication to other unused frequencies. Unlike previous works that leverage static techniques, DEMIS dynamically targets specific frequency bands; the type of techniques used here are only possible from an architectural perspective. This paper is also the first to provide insights in the new area of dynamic EMI shifting by evaluating several platforms and showing the EMI is sensitive to many architectural and compilation parameters. Our evaluation over real systems shows a decrease of in-band EMI ranging from 3 to 15 dB with less than a 10% average performance impact. A 15dB EMI reduction for LTE can represent over 3x bandwidth improvement for EMI bound communication. CCS CONCEPTS • Hardware → Noise reduction; Wireless devices; Signal integrity and noise analysis;
Processors radiate electromagnetic interference (EMI), which affects wireless communication technologies. However, despite the fact that the EMI generated by a processor is deterministic, architecturally modeling the EMI has proven to be a complex challenge. Moreover, EMI depends on the physical layout of the processor and on the binary being executed (both the application and its compilation options). This paper proposes Model for EMI on a SoC (MESC), the first architectural framework for modeling electromagnetic emissions from a core. MESC takes into account the layout and the switching activity of a process to model the expected EMI. We validate MESC on a real system to verify its accuracy. We then use MESC to demonstrate that two different core layouts can be leveraged to reduce EMI and propose EMI Core Hopper (EMI CHopper). EMI CHopper uses a multi-core system-where each core has the same RTL but minimally different layouts-and proposes hopping the application between cores to reduce in-band EMI when it interferes with wireless communication. Our evaluation shows that MESC is able to predict EMI within 95% accuracy across time and across the frequency spectrum, even when using statistical sampling to obtain activity rates. Leveraging MESC, our proposed EMI CHopper reduces in-band EMI by up to 50%, with low impact on performance. MESC will enable a new stream of micro-architectural research the same way architectural level power models have enabled exploration of performance and power simulation. CCS CONCEPTS • Computing methodologies → Model development and analysis; Simulation evaluation; • Computer systems organization → Multicore architectures.
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