14.6 An all-digital power-delivery monitor for analysis of a 28nm dual-core ARM Cortex-A57 cluster

Measuring and Exploiting Guardbands of Server-Grade ARMv8 CPU Cores and DRAMs

“…Cache viruses were crafted to exploit the underlying microarchitecture and test all levels of the cache hierarchy, while core viruses are being generated by genetic algorithms. To stress the cores, we use dI/dt viruses that cause the CPU power consumption to switch between high and low power at a rate equal to PDN 1 st order resonant frequency [2,8,14]. This causes maximum voltage noise.…”

“…Such margins are becoming more prominent with the use of more cores per chip and technology scaling. These technology trends exacerbate core-to-core variations, voltage droops [2,3], reliability issues [2] and SRAM malfunctions [15,16] at low voltages (Vmin).…”

“…We measure the guradbands in 8 cores of ARMv8 CPU chips, and 3 different sigma chips manufactured in 28nm process based on an automated characterization methodology and by using various synthetic benchmarks and applications. To measure voltage guardbands, it is essential to craft worst-case voltage noise stress tests (also known as dI/dt viruses) that expose worst-case voltage droops [2,8,13]. Typically, these stress-tests are automatically generated using optimization approaches, such as Genetic Algorithms (GA), guided by direct voltage measurements [2,8].…”

“…To measure voltage guardbands, it is essential to craft worst-case voltage noise stress tests (also known as dI/dt viruses) that expose worst-case voltage droops [2,8,13]. Typically, these stress-tests are automatically generated using optimization approaches, such as Genetic Algorithms (GA), guided by direct voltage measurements [2,8]. Since X-Gene2 doesn't support fine-grained voltage measurements, to generate dI/dt viruses, we use an alternative methodology which is based on sensing high voltage noise through CPU electromagnetic emanations (EM) [14].…”

“…This is achieved by exploiting architectural and micro-architectural characteristics of the X-Gene2 platform and ARMv8 ISA. Workload variations are also present as different workload cause different voltage noise [2,3,8,14]. To capture these workload variations, we perform a comprehensive characterization using real workloads, including SPEC2006 and NAS benchmark suites in both singleprocess and multi-process setups.…”