On 03/09/2019 16:43, Radim Krčmář wrote: > The paper "The Linux Scheduler: a Decade of Wasted Cores" used several > custom data gathering points to better understand what was going on in > the scheduler. > Red Hat adapted one of them for the tracepoint framework and created a > tool to plot a heatmap of nr_running, where the sched_update_nr_running > tracepoint is being used for fine grained monitoring of scheduling > imbalance. > The tool is available from https://github.com/jirvoz/plot-nr-running. > > The best place for the tracepoints is inside the add/sub_nr_running, > which requires some shenanigans to make it work as they are defined > inside sched.h. > The tracepoints have to be included from sched.h, which means that > CREATE_TRACE_POINTS has to be defined for the whole header and this > might cause problems if tree-wide headers expose tracepoints in sched.h > dependencies, but I'd argue it's the other side's misuse of tracepoints. > > Moving the import sched.h line lower would require fixes in s390 and ppc > headers, because they don't include dependecies properly and expect > sched.h to do it, so it is simpler to keep sched.h there and > preventively undefine CREATE_TRACE_POINTS right after. > > Exports of the pelt tracepoints remain because they don't need to be > protected by CREATE_TRACE_POINTS and moving them closer would be > unsightly. >
Pure trace events are frowned upon in scheduler world, try going with trace points. Qais did something very similar recently: https://lore.kernel.org/lkml/20190604111459.2862-1-qais.you...@arm.com/ You'll have to implement the associated trace events in a module, which lets you define your own event format and doesn't form an ABI :).