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

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Date:	Thu, 27 Jun 2013 07:56:57 -0600
From:	David Ahern <dsahern@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
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 6/26/13 11:23 PM, Namhyung Kim wrote:
> 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.

Could that ever change? With the current code why call it pid in the 
option but assign it to target.tid? Seems a like a source for confusion 
later. Would be better to just assign to target.pid and let the 
machinery do the right thing.

David

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