linux-kernel - Re: [PATCH] [perf] intel_pt_recording_options: Remove redundant intel_pt

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Date:   Wed, 24 Jun 2020 19:05:03 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Jiri Olsa <jolsa@...hat.com>, Gaurav Singh <gaurav1086@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Ian Rogers <irogers@...gle.com>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [perf] intel_pt_recording_options: Remove redundant
 intel_pt_evsel null check

On 24/06/20 3:42 pm, Jiri Olsa wrote:
> On Tue, Jun 23, 2020 at 07:48:50PM -0400, Gaurav Singh wrote:
>> intel_pt_evsel cannot be NULL here since its already being
>> dereferenced above. Remove this redundant check.
>>
>> Signed-off-by: Gaurav Singh <gaurav1086@...il.com>
>> ---
>>  tools/perf/arch/x86/util/intel-pt.c | 24 +++++++++++-------------
>>  1 file changed, 11 insertions(+), 13 deletions(-)
>>
>> diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
>> index 839ef52c1ac2..8cc87fd2dc6f 100644
>> --- a/tools/perf/arch/x86/util/intel-pt.c
>> +++ b/tools/perf/arch/x86/util/intel-pt.c
>> @@ -836,19 +836,17 @@ static int intel_pt_recording_options(struct auxtrace_record *itr,
>>  		}
>>  	}
>>  
> 
> I wonder we sould put check before that above usage of intel_pt_evsel,
> because there's no check for that.. but yes, if intel_pt_evsel is NULL
> it will fail earlier.. Adrian?

The code was written when sampling-mode did not require an intel_pt_evsel.
Now it does, so intel_pt_evsel will not be NULL.  I think it is OK as is.

> 
> thanks,
> jirka
> 
>> -	if (intel_pt_evsel) {
>> -		/*
>> -		 * To obtain the auxtrace buffer file descriptor, the auxtrace
>> -		 * event must come first.
>> -		 */
>> -		perf_evlist__to_front(evlist, intel_pt_evsel);
>> -		/*
>> -		 * In the case of per-cpu mmaps, we need the CPU on the
>> -		 * AUX event.
>> -		 */
>> -		if (!perf_cpu_map__empty(cpus))
>> -			evsel__set_sample_bit(intel_pt_evsel, CPU);
>> -	}
>> +	/*
>> +	 * To obtain the auxtrace buffer file descriptor, the auxtrace
>> +	 * event must come first.
>> +	 */
>> +	perf_evlist__to_front(evlist, intel_pt_evsel);
>> +	/*
>> +	 * In the case of per-cpu mmaps, we need the CPU on the
>> +	 * AUX event.
>> +	 */
>> +	if (!perf_cpu_map__empty(cpus))
>> +		evsel__set_sample_bit(intel_pt_evsel, CPU);
>>  
>>  	/* Add dummy event to keep tracking */
>>  	if (opts->full_auxtrace) {
>> -- 
>> 2.17.1
>>
>