linux-kernel - Re: [PATCH 2/2] perf: Fix ftrace builtin when kernel doesn't have function

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Message-ID: <047da0c7-6552-e6bb-d044-7cb5e05c431d@arm.com>
Date:   Wed, 1 Nov 2017 16:58:20 +0000
From:   Julien Thierry <julien.thierry@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-arm-kernel@...ts.infradead.org, takahiro.akashi@...aro.org,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] perf: Fix ftrace builtin when kernel doesn't have
 function_graph



On 01/11/17 16:44, Steven Rostedt wrote:
> On Wed,  1 Nov 2017 14:33:44 +0000
> Julien Thierry <julien.thierry@....com> wrote:
> 
>> When linux is built without support for function graph tracer, the ftrace
>> builtin of perf will fail when trying to reset max_graph_depth because the
>> file does not exist. This prevents the use of function tracer from perf.
>>
>> Do not attempt to write this file when the tracer in use is not
>> function_graph.
>>
>> Signed-off-by: Julien Thierry <julien.thierry@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>   tools/perf/builtin-ftrace.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
>> index 25a42ac..48120f2 100644
>> --- a/tools/perf/builtin-ftrace.c
>> +++ b/tools/perf/builtin-ftrace.c
>> @@ -130,7 +130,8 @@ static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
>>   	if (reset_tracing_cpu() < 0)
>>   		return -1;
>>
>> -	if (write_tracing_file("max_graph_depth", "0") < 0)
>> +	if (!strcmp(ftrace->tracer, "function_graph") &&
>> +	    write_tracing_file("max_graph_depth", "0") < 0)
> 
> Hmm, instead of doing this, could we just do a stat on the file first.
> As with trace-cmd, I like to reset files like this even when not
> enabling function_graph tracer.
> 

Sounds reasonable.

I'll include that change in the next version of the patches.

Thanks,

-- 
Julien Thierry