linux-kernel - Re: [PATCH v1 1/2] perf callchain lbr: Make the leaf IP that of the sample

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Message-ID: <aYZYrxyg7MTepxKQ@x1>
Date: Fri, 6 Feb 2026 18:10:07 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
Cc: Ian Rogers <irogers@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>,
	Krzysztof Łopatowski <krzysztof.m.lopatowski@...il.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Weilin Wang <weilin.wang@...el.com>
Subject: Re: [PATCH v1 1/2] perf callchain lbr: Make the leaf IP that of the
 sample

On Fri, Feb 06, 2026 at 09:44:04AM +0800, Mi, Dapeng wrote:
> 
> On 2/6/2026 4:56 AM, Ian Rogers wrote:
> > The current IP of a leaf function when reported from a perf record
> > with "--call-graph lbr" is the "to" field of the LBR branch stack
> > record. The sample for the event being recorded may be further into
> > the function and there may be inlining information associated with
> > it. Rather than use the branch stack "to" field in this case switch to
> > the callchain appending the sample->ip and thereby allowing the inline
> > information to show.
> >
> > Before this change:
> > ```
> > $ perf record --call-graph lbr perf test -w inlineloop
> > ...
> > $ perf script --fields +srcline
> > ...
> > perf-inlineloop  467586  4649.344493:     950905 cpu_core/cycles/P:
> >            55dfda2829c0 parent+0x0 (perf)
> >  inlineloop.c:31
> >            55dfda282a96 inlineloop+0x86 (perf)
> >  inlineloop.c:47
> >            55dfda236420 run_workload+0x59 (perf)
> >  builtin-test.c:715
> >            55dfda236b03 cmd_test+0x413 (perf)
> >  builtin-test.c:825
> > ...
> > ```
> >
> > After this change:
> > ```
> > $ perf record --call-graph lbr perf test -w inlineloop
> > ...
> > $ perf script --fields +srcline
> > ...
> > perf-inlineloop  529703 11878.680815:     950905 cpu_core/cycles/P:
> >             555ce86be9e6 leaf+0x26
> >   inlineloop.c:20 (inlined)
> >             555ce86be9e6 middle+0x26
> >   inlineloop.c:27 (inlined)
> >             555ce86be9e6 parent+0x26 (perf)
> >   inlineloop.c:32
> >             555ce86bea96 inlineloop+0x86 (perf)
> >   inlineloop.c:47
> >             555ce8672420 run_workload+0x59 (perf)
> >   builtin-test.c:715
> >             555ce8672b03 cmd_test+0x413 (perf)
> >   builtin-test.c:825
> > ...
> > ```
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/perf/util/machine.c | 20 ++++++++++++++++----
> >  1 file changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > index 5b0f5a48ffd4..e76f8c86e62a 100644
> > --- a/tools/perf/util/machine.c
> > +++ b/tools/perf/util/machine.c
> > @@ -2423,8 +2423,14 @@ static int lbr_callchain_add_lbr_ip(struct thread *thread,
> >  	}
> >  
> >  	if (callee) {
> > -		/* Add LBR ip from first entries.to */
> > -		ip = entries[0].to;
> > +		/*
> > +		 * Set the (first) leaf function's IP to sample->ip (the
> > +		 * location of the sample) but if not recorded use entries.to
> > +		 */
> > +		if (sample->ip)
> > +			ip = sample->ip;
> > +		else
> > +			ip = entries[0].to;
> >  		flags = &entries[0].flags;
> >  		*branch_from = entries[0].from;
> >  		err = add_callchain_ip(thread, cursor, parent,
> > @@ -2477,8 +2483,14 @@ static int lbr_callchain_add_lbr_ip(struct thread *thread,
> >  	}
> >  
> >  	if (lbr_nr > 0) {
> > -		/* Add LBR ip from first entries.to */
> > -		ip = entries[0].to;
> > +		/*
> > +		 * Set the (first) leaf function's IP to sample->ip (the
> > +		 * location of the sample) but if not recorded use entries.to
> > +		 */
> > +		if (sample->ip)
> > +			ip = sample->ip;
> > +		else
> > +			ip = entries[0].to;
> >  		flags = &entries[0].flags;
> >  		*branch_from = entries[0].from;
> >  		err = add_callchain_ip(thread, cursor, parent,
> 
> LGTM. Thanks.

Next time please express that with an Acked-by, that way b4 will collect
it.

I'm adding it this time:

Acked-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>

ok?

- Arnaldo