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

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Message-ID: <d3f95dcc-4b55-4110-86be-a79f68fab7b9@linux.intel.com>
Date: Mon, 9 Feb 2026 08:43:41 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
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 2/7/2026 5:10 AM, Arnaldo Carvalho de Melo wrote:
> 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?

Yeah. Thanks.


>
> - Arnaldo
>
>