Title: Transkernel: An Executor for Commodity Kernels on Peripheral Cores,
Abstract: Modern mobile and embedded platforms see a large number of ephemeral tasks
driven by background activities. In order to execute such a task, the OS kernel
wakes up the platform beforehand and puts it back to sleep afterwards. In doing
so, the kernel operates various IO devices and orchestrates their power state
transitions. Such kernel execution phases are lengthy, having high energy cost,
and yet difficult to optimize. We advocate for relieving the CPU from these
kernel phases by executing them on a low-power, microcontroller-like core,
dubbed peripheral core, hence leaving the CPU off. Yet, for a peripheral core
to execute phases in a complex commodity kernel (e.g. Linux), existing
approaches either incur high engineering effort or high runtime overhead. We
take a radical approach with a new executor model called transkernel. Running
on a peripheral core, a transkernel executes the binary of the commodity kernel
through cross-ISA, dynamic binary translation (DBT). The transkernel translates
stateful kernel code while emulating a small set of stateless kernel services;
it sets a narrow, stable binary interface for emulated services; it specializes
for kernel's beaten paths; it exploits ISA similarities for low DBT cost. With
a concrete implementation on a heterogeneous ARM SoC, we demonstrate the
feasibility and benefit of transkernel. Our result contributes a new OS
structure that combines cross-ISA DBT and emulation for harnessing a
heterogeneous SoC. Our result demonstrates that while cross-ISA DBT is
typically used under the assumption of efficiency loss, it can be used for
efficiency gain, even atop off-the-shelf hardware.