On Freitag, 22. April 2022 07:33:57 CEST Namhyung Kim wrote: > Hello, > > This is the first version of off-cpu profiling support. Together with > (PMU-based) cpu profiling, it can show holistic view of the performance > characteristics of your application or system. Hey Namhyung, this is awesome news! In hotspot, I've long done off-cpu profiling manually by looking at the time between --switch-events. The downside is that we also need to track the sched:sched_switch event to get a call stack. But this approach also works with dwarf based unwinding, and also includes kernel stacks. > With BPF, it can aggregate scheduling stats for interested tasks > and/or states and convert the data into a form of perf sample records. > I chose the bpf-output event which is a software event supposed to be > consumed by BPF programs and renamed it as "offcpu-time". So it > requires no change on the perf report side except for setting sample > types of bpf-output event. > > Basically it collects userspace callstack for tasks as it's what users > want mostly. Maybe we can add support for the kernel stacks but I'm > afraid that it'd cause more overhead. So the offcpu-time event will > always have callchains regardless of the command line option, and it > enables the children mode in perf report by default. Has anything changed wrt perf/bpf and user applications not compiled with `- fno-omit-frame-pointer`? I.e. does this new utility only work for specially compiled applications, or do we also get backtraces for "normal" binaries that we can install through package managers? Thanks -- Milian Wolff | milian.wolff@xxxxxxxx | Senior Software Engineer KDAB (Deutschland) GmbH, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt, C++ and OpenGL Experts
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