Energy efficiency is a known major concern for computing system
designers. Significant effort is devoted to power optimization of modern
systems, especially in large-scale installations such as data centers,
in which both high performance and energy efficiency are important.
Power optimization can be achieved through different approaches, several
of which focus on adaptive voltage regulation. In this paper, we present
a comprehensive exploration of how two server-grade systems behave in
different frequency and core allocation configurations beyond nominal
voltage operation. Our analysis, which is built on top of two
state-of-the-art ARMv8 microprocessor chips (Applied Micro’s X-Gene 2
and X-Gene 3) aims (1) to identify the best performance per watt
operation points when the servers are operating in various
voltage/frequency combinations, (2) to reveal how and why the different
core allocation options on the available cores of the microprocessor
affect the energy consumption, and (3) to enhance the default Linux
scheduler to take task allocation decisions for balanced performance and
energy efficiency. Our findings, on actual servers’ hardware, have been
integrated into a lightweight online monitoring daemon which decides the
optimal combination of voltage, core allocation, and clock frequency to
achieve higher energy efficiency. Our approach reduces on average the
energy by 25.2% on X-Gene 2, and 22.3% on X-Gene 3, with a minimal
performance penalty of 3.2% on X-Gene 2 and 2.5% on X-Gene 3, compared
to the default system configuration