linux-kernel - Re: [PATCH 0/1] perf report: append inlines to non-dwarf callchains

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Message-ID: <ZCs3WX4klUpe+aso@kernel.org>
Date:   Mon, 3 Apr 2023 17:30:17 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Artem Savkov <asavkov@...hat.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Milian Wolff <milian.wolff@...b.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH 0/1] perf report: append inlines to non-dwarf callchains

Em Fri, Mar 31, 2023 at 10:52:24AM +0200, Artem Savkov escreveu:
> On Thu, Mar 30, 2023 at 08:06:20AM +0300, Adrian Hunter wrote:
> > On 22/03/23 21:44, Arnaldo Carvalho de Melo wrote:
> > > Em Wed, Mar 22, 2023 at 11:18:49AM -0700, Namhyung Kim escreveu:
> > >> On Fri, Mar 17, 2023 at 12:41 AM Artem Savkov <asavkov@...hat.com> wrote:
> > >>>
> > >>> On Thu, Mar 16, 2023 at 02:26:18PM -0700, Namhyung Kim wrote:
> > >>>> Hello,
> > >>>>
> > >>>> On Thu, Mar 16, 2023 at 6:36 AM Artem Savkov <asavkov@...hat.com> wrote:
> > >>>>>
> > >>>>> In an email to Arnaldo Andrii Nakryiko suggested that perf can get
> > >>>>> information about inlined functions from dwarf when available and then
> > >>>>> add it to userspace stacktraces even in framepointer or lbr mode.
> > >>>>> Looking closer at perf it turned out all required bits and pieces are
> > >>>>> already there and inline information can be easily added to both
> > >>>>> framepointer and lbr callchains by adding an append_inlines() call to
> > >>>>> add_callchain_ip().
> > >>>>
> > >>>> Looks great!  Have you checked it with perf report -g callee ?
> > >>>> I'm not sure the ordering of inlined functions is maintained
> > >>>> properly.  Maybe you can use --no-children too to simplify
> > >>>> the output.
> > >>>
> > >>> Thanks for the suggestion. I actually have another test program with
> > >>> functions being numbered rather than (creatively) named, so it might be
> > >>> easier to use it to figure out ordering. Here's the code:
> > >>
> > >> Yep, looks good.
> > >>
> > >> Acked-by: Namhyung Kim <namhyung@...nel.org>
> > > 
> > > So, I'll apply this shorter patch instead, ok?
> > > 
> > > - Arnaldo
> > > 
> > > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > > index 803c9d1803dd26ef..abf6167f28217fe6 100644
> > > --- a/tools/perf/util/machine.c
> > > +++ b/tools/perf/util/machine.c
> > > @@ -44,6 +44,7 @@
> > >  #include <linux/zalloc.h>
> > >  
> > >  static void __machine__remove_thread(struct machine *machine, struct thread *th, bool lock);
> > > +static int append_inlines(struct callchain_cursor *cursor, struct map_symbol *ms, u64 ip);
> > >  
> > >  static struct dso *machine__kernel_dso(struct machine *machine)
> > >  {
> > > @@ -2322,6 +2323,10 @@ static int add_callchain_ip(struct thread *thread,
> > >  	ms.maps = al.maps;
> > >  	ms.map = al.map;
> > >  	ms.sym = al.sym;
> > > +
> > > +	if (append_inlines(cursor, &ms, ip) == 0)
> > > +		return 0;
> > > +
> > >  	srcline = callchain_srcline(&ms, al.addr);
> > >  	return callchain_cursor_append(cursor, ip, &ms,
> > >  				       branch, flags, nr_loop_iter,
> > 
> > This seems to be breaking --branch-history.  I am not sure
> > append_inlines() makes sense for branches.  Maybe this should be:
> > 
> > 	if (!branch && !append_inlines(cursor, &ms, ip))
> > 		return 0;
> > 
> 
> Right. So when cllchain_cursor is appended through append_inlines it
> always discards branch information, even for the non-inlined function.
> So adding !branch makes sense to me. Does anyone else see any problems
> with that?

I'm no expert in this specific area, so for now till we get to a
conclusion on this, I'll follow Andi's suggestion and revert this patch.

- Arnaldo