linux-kernel - Re: [PATCH v5 03/17] perf ftrace: add option -t/--tid to filter by thread id

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Date:   Fri, 17 Jul 2020 21:26:50 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Changbin Du <changbin.du@...il.com>, Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 03/17] perf ftrace: add option -t/--tid to filter by
 thread id

On Thu, Jul 16, 2020 at 12:36:30PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sat, Jul 11, 2020 at 08:40:21PM +0800, Changbin Du escreveu:
> > This allows us to trace single thread instead of the whole process.
> > 
> > Signed-off-by: Changbin Du <changbin.du@...il.com>
> > ---
> >  tools/perf/Documentation/perf-ftrace.txt | 4 ++++
> >  tools/perf/builtin-ftrace.c              | 2 ++
> >  2 files changed, 6 insertions(+)
> > 
> > diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
> > index d79560dea19f..e204bf6d50d8 100644
> > --- a/tools/perf/Documentation/perf-ftrace.txt
> > +++ b/tools/perf/Documentation/perf-ftrace.txt
> > @@ -38,6 +38,10 @@ OPTIONS
> >  --pid=::
> >  	Trace on existing process id (comma separated list).
> >  
> > +-t::
> > +--tid=::
> > +	Trace on existing thread id (comma separated list).
> > +
> 
> 
> Humm, I just  tried:
> 
> [root@...e ~]# yes > /dev/null &
> [1] 18265
> [root@...e ~]# perf ftrace --tid 18265
> ^C[root@...e ~]#
> 
> After waiting for a while, nothing, what am I doing wrong?
>
I got it wrong. Currently ftrace only can filter by pid. If the pid is not
the main thread it won't work.

So this patch makes no sense. will drop this.

> - Arnaldo
> 
> 
> >  -a::
> >  --all-cpus::
> >  	Force system-wide collection.  Scripts run without a <command>
> > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> > index 244cc8e6bd60..1188b82c6541 100644
> > --- a/tools/perf/builtin-ftrace.c
> > +++ b/tools/perf/builtin-ftrace.c
> > @@ -515,6 +515,8 @@ int cmd_ftrace(int argc, const char **argv)
> >  		    "Show available functions to filter"),
> >  	OPT_STRING('p', "pid", &ftrace.target.pid, "pid",
> >  		   "trace on existing process id"),
> > +	OPT_STRING('t', "tid", &ftrace.target.tid, "tid",
> > +		   "trace on existing thread id (exclusive to --pid)"),
> >  	OPT_INCR('v', "verbose", &verbose,
> >  		 "be more verbose"),
> >  	OPT_BOOLEAN('a', "all-cpus", &ftrace.target.system_wide,
> > -- 
> > 2.25.1
> > 
> 
> -- 
> 
> - Arnaldo

-- 
Cheers,
Changbin Du