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

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Message-ID: <764406ae-c604-410c-9205-7f3343a4bd8f@linux.intel.com>
Date: Fri, 6 Feb 2026 09:44:04 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 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 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.