linux-kernel - Re: [PATCH 06/19] perf ftrace: Add support for --pid option

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Date:	Thu, 27 Jun 2013 14:23:46 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 06/19] perf ftrace: Add support for --pid option

On Wed, 26 Jun 2013 11:12:19 -0600, David Ahern wrote:
> On 6/26/13 1:14 AM, Namhyung Kim wrote:
>> @@ -196,6 +222,8 @@ int cmd_ftrace(int argc, const char **argv, const char *prefix __maybe_unused)
>>   	const struct option ftrace_options[] = {
>>   	OPT_STRING('t', "tracer", &ftrace.tracer, "tracer",
>>   		   "tracer to use"),
>> +	OPT_STRING('p', "pid", &ftrace.target.tid, "pid",
>> +		   "trace on existing process id"),
>>   	OPT_INCR('v', "verbose", &verbose,
>>   		 "be more verbose"),
>>   	OPT_END()
>
> You are calling it pid but assigning it as a tid which is inconsistent
> with other perf commands. e.g., perf-record allows a list of pids (-p)
> or tids (-t). Why not support that in perf-ftrace? And that leads to
> the comment about consistency of options across perf commands: -t is
> used here for tracer type to use.

Sorry, I should've mentioned it.

The pid filtering in ftrace is done via set_ftrace_pid file under the
tracing debugfs directory.  IIRC It only supports process filtering not
thread filtering by iterating all threads in the kernel code.  So --tid
option cannot be implemented as other perf commands.

So I chose not to and assigned -t option to --tracer.

Thanks,
Namhyung
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