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Message-ID: <CAP-5=fWZVHN5tDG+eKRr7v_RXKYA_uUgY-dFH_g3Yc3mFgkXbA@mail.gmail.com>
Date: Wed, 30 Nov 2022 12:13:10 -0800
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Leo Yan <leo.yan@...aro.org>,
Kan Liang <kan.liang@...ux.intel.com>,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 3/4] perf build: Use libtraceevent from the system
On Wed, Nov 30, 2022 at 11:05 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Tue, Nov 29, 2022 at 10:30 PM Ian Rogers <irogers@...gle.com> wrote:
> >
> > Remove the LIBTRACEEVENT_DYNAMIC and LIBTRACEFS_DYNAMIC. If
> > libtraceevent isn't installed or NO_LIBTRACEEVENT=1 is passed to the
> > build, don't compile in libtraceevent and libtracefs support. This
> > also disables CONFIG_TRACE that controls "perf
> > trace". CONFIG_TRACEEVENT is used to control enablement in
> > Build/Makefiles, HAVE_LIBTRACEEVENT is used in C code. Without
> > HAVE_LIBTRACEEVENT tracepoints are disabled and as such the commands
> > kmem, kwork, lock, sched and timechart are removed. The majority of
> > commands continue to work including "perf test".
>
> Maybe we can have a different approach. I guess the trace data
> access is isolated then we can make dummy interfaces when there's
> no libtraceevent. This way we don't need to touch every command
> and let it fail when it's asked.
Sounds like a worthwhile refactor that can land on top of this change.
> The motivation is that we should be able to run the sub-commands
> as much as possible. In fact, we could run 'record' part only on the
> target machine and pass the data to the host for analysis with a
> full-fledged perf. Also some commands like 'perf lock contention'
> can run with or without libtraceevent (using BPF only).
The issue here is that perf lock contention will use evsel__new_tp and
internally that uses libtraceevent. As such it is removed without
HAVE_LIBTRACEEVENT. Without the evsel there's not much perf lock
contention can do, so rather than litter the code with
HAVE_LIBTRACEEVENT and for it to be broken, I made the choice just to
remove it from the no libtraceevent build for now.
I think it is worth pursuing these patches in the shape they are in so
that we can land the removal of tools/lib/traceevent and ensure the
migration away from an out-of-date version of that library.
Thanks,
Ian
> Thanks,
> Namhyung
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