Fluid kernels: seamlessly conquering the embedded computing continuum

To achieve seamless portability across the embedded computing continuum, we introduce a new kernel architecture: fluid kernels. Fluid kernels can be thought of as the intersection between embedded unikernels and general purpose monolithic kernels, allowing to seamlessly develop applications both in kernel space and user space in a unified way. This scalable kernel architecture can manage the trade-off between performance, code size, isolation and security. We compare our fluid kernel implementation, Miosix, to Linux and FreeRTOS on the same hardware with standard benchmarks. Compared to Linux, we achieve an average speedup of 3.5x and a maximum of up to 15.4x. We also achieve an average code size reduction of 84% and a maximum of up to 90%. By moving application code from user space to kernel space, an additional code size reduction up to 56% and a speedup up to 1.3x can be achieved. Compared to FreeRTOS, the use of Miosix only costs a moderate amount of code size (at most 47KB) for significant advantages in application performance with speedups averaging at 1.5x and up to 5x.