Em Tue, Dec 29, 2020 at 05:14:12PM +0000, Song Liu escreveu: > > On Dec 29, 2020, at 3:48 AM, Arnaldo Carvalho de Melo <a...@kernel.org> > > wrote:
> > Em Tue, Dec 29, 2020 at 04:01:41PM +0900, Namhyung Kim escreveu: > >> On Tue, Dec 29, 2020 at 2:41 AM Song Liu <songliubrav...@fb.com> wrote: > >>> BPF programs are useful in perf to profile BPF programs. BPF skeleton is > >> I'm having difficulties understanding the first sentence - looks like a > >> recursion. :) So do you want to use two (or more) BPF programs? > > Yeah, we use perf to perf perf, so we need to use bpf with perf to perf > > bpf :-) > > Look at tools/perf/util/bpf_skel/bpf_prog_profiler.bpf.c, the BPF > > skeleton used to create the in-kernel scaffold to profile BPF programs. > > It uses two BPF programs (fentry/XXX and fexit/XXX) and some a s/some// > > PERF_EVENT_ARRAY map and an array to diff counters read at exit from > > counters read at exit of the profiled BPF programs and then accumulate s/exit/entry/ > > those diffs in another PERCPU_ARRAY. > > This all ends up composing a "BPF PMU" that is what the userspace perf > > tooling will read (from "accum_readings" BPF map) and 'perf stat' will > > consume as if reading from an "old style perf counter" :-) > > Song, did I get it right? :-) > Thanks Arnaldo! I don't think anyone can explain it better. :-) There, a patch :-) - Arnaldo