Micro-Viruses for Fast System-Level Voltage Margins Characterization in Multicore CPUs

In this paper, we propose the employment of fast targeted programs (diagnostic micro-viruses) that aim to stress individually the main hardware components of a multicore CPU architecture which most likely determine the limits of voltage scaling, i.e. safe Vmin values. We describe in detail the complex development process for the diagnostic micro-viruses and their comprehensive validation in modern multicore CPU hardware. The combined execution of the micro-viruses takes very short time compared to regular programs execution, and can quickly reveal the voltage limits of the cores and chips at voltage levels below nominal. The micro-virus based characterization flow requires orders of magnitude shorter time while it delivers virtually identical: (a) Vmin values for the different CPU chips, and (b) Vmin values for the different cores within a CPU chip. We evaluate our micro-viruses based characterization flow (and compare it to the SPEC-based flow) on three different chips (a nominal graded and two corner parts) of Applied Micro's X-Gene 2 micro-server family (with 8-core ARMv8-based CPUs manufactured in 28nm). We report detailed validation and evaluation results that prove the effectiveness of the micro-viruses for the fast and accurate identification of the voltage margins variability among the chips and the cores of a multicore CPU.