Fork/Wait and Multicore Frequency Scaling: a Generational Clash

International audienceThe complexity of computer architectures has risen since the early years of the Linux kernel: Simultaneous Multi-Threading (SMT), multicore processing, and frequency scaling with complex algorithms such as Intel ® Turbo Boost have all become omnipresent. In order to keep up with hardware innovations, the Linux scheduler has been rewritten several times, and many hardware-related heuristics have been added. Despite this, we show in this paper that a fundamental problem was never identified: the POSIX process creation model, i.e., fork/wait, can behave inefficiently on current multicore architectures due to frequency scaling. We investigate this issue through a simple case study: the compilation of the Linux kernel source tree. To do this, we develop SchedLog, a low-overhead scheduler tracing tool, and SchedDisplay, a scriptable tool to graphically analyze SchedLog's traces efficiently. We implement two solutions to the problem at the sched-uler level which improve the speed of compiling part of the Linux kernel by up to 26%, and the whole kernel by up to 10%