linux-kernel - Re: [BUG] perf: intel_pt won't display kernel function

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Date:   Wed, 3 Apr 2019 16:27:56 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
CC:     Jiri Olsa <jolsa@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <andi@...stfloor.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [BUG] perf: intel_pt won't display kernel function



> On Apr 3, 2019, at 8:15 AM, Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> wrote:
> 
> Em Wed, Apr 03, 2019 at 11:53:53AM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Wed, Apr 03, 2019 at 04:37:38PM +0200, Jiri Olsa escreveu:
>>> hi,
>>> perf script --call-trace stop working for me recently,
>>> and displays only user space functions
>>> 
>>> I bisected that to:
>>>  7b612e291a5a perf tools: Synthesize PERF_RECORD_* for loaded BPF programs
>>> 
>>> data from following comands will display user space functions only:
>>>  # perf-with-kcore record pt -e intel_pt// -- ls
>>>  # perf-with-kcore script pt --call-trace
>>> 
>>> when I disable the bpf synthesizing (patch below), kernel functions are back
>>> 
>>> I guess the new events mess up with intel_pt decoder somehow
>> 
>> I.e. I'm adding the patch below to my perf/urgent branch.
> 
> Song, that is what I have, can I have your Acked-by and please consider
> taking a look at the bug Jiri reported,
> 
> Thanks,
> 
> - Arnaldo

Current logic with --no-bpf-event is to generate PERF_RECORD_KSYMBOL, but not
PERF_RECORD_BPF_EVENT:

https://elixir.bootlin.com/linux/v5.1-rc3/source/tools/perf/util/bpf-event.c#L254

I will look into the intel_pt problem. 

In the meanwhile, let's fix it for now. 

Acked-by: Song Liu <songliubraving@...com>

Thanks, 
Song


> commit 011318ccc2024ba03e96c32a06f74ca5d6ab5503
> Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> Date:   Wed Apr 3 12:05:15 2019 -0300
> 
>    perf record: Do not synthesize BPF records when --no-bpf-event is used
> 
>    By default we synthesize and ask the kernel for BPF events, having a
>    --no-bpf-event option to disable that, which can be useful, for
>    instance, if there are still bugs in that code, which seems to be the
>    case as reported by Jiri Olsa in:
> 
>      "[BUG] perf: intel_pt won't display kernel function"
>      https://lore.kernel.org/lkml/20190403143738.GB32001@krava
> 
>    So add the check for record_opts.no_bpf_event when considering
>    synthesizing BPF events for pre-existing BPF programs in 'perf record'.
> 
>    The reported bug needs further analysis and is a separate matter.
> 
>    Cc: Adrian Hunter <adrian.hunter@...el.com>
>    Cc: Alexei Starovoitov <ast@...nel.org>
>    Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
>    Cc: Daniel Borkmann <daniel@...earbox.net>
>    Cc: Jiri Olsa <jolsa@...nel.org>
>    Cc: Martin KaFai Lau <kafai@...com>
>    Cc: Namhyung Kim <namhyung@...nel.org>
>    Cc: Peter Zijlstra <peterz@...radead.org>
>    Cc: Song Liu <songliubraving@...com>
>    Cc: Yonghong Song <yhs@...com>
>    Fixes: 7b612e291a5a ("perf tools: Synthesize PERF_RECORD_* for loaded BPF programs")
>    Link: https://lore.kernel.org/lkml/20190403145353.GE32553@kernel.org
>    Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 4e2d953d4bc5..17d772f192ad 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1114,10 +1114,11 @@ static int record__synthesize(struct record *rec, bool tail)
> 		return err;
> 	}
> 
> -	err = perf_event__synthesize_bpf_events(session, process_synthesized_event,
> -						machine, opts);
> -	if (err < 0)
> -		pr_warning("Couldn't synthesize bpf events.\n");
> +	if (!opts->no_bpf_event) {
> +		err = perf_event__synthesize_bpf_events(session, process_synthesized_event, machine, opts);
> +		if (err < 0)
> +			pr_warning("Couldn't synthesize bpf events.\n");
> +	}
> 
> 	err = __machine__synthesize_threads(machine, tool, &opts->target, rec->evlist->threads,
> 					    process_synthesized_event, opts->sample_address,