Lazy Scheduling and Direct Process Switch --- Merit or Myths?
Kevin Elphinstone, David Greenaway and Sergio Ruocco
Workshop on Operating Systems Platforms for Embedded Real-Time applications (OSPERT 2007)
Pisa, Italy, July 3, 2007
Summary
The L4 microkernel, like many first and second generation microkernels, was designed to maximise best-effort performance. One component of its functionality critical to overall system performance is its interprocess communication. L4 uses two techniques to minimise communication costs: direct process switching and lazy scheduling. These techniques improve performance at the expense of real-time predictability of the scheduler. Now that L4 is being adopted in the embedded space, which features real-time requirements, we must determine if there is continued merit in using the optimisations. We quantitatively analyse the two optimisations using different kernel implementations and measure the performance improvements of the optimisations directly, and indirectly using the Re-aim benchmark suite.