linux-kernel - Re: [PATCH v3 00/27] function_graph: Allow multiple users for function graph tracing

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Date: Tue, 4 Jun 2024 14:57:42 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mark Rutland <mark.rutland@....com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Alexei Starovoitov
 <alexei.starovoitov@...il.com>, Florent Revest <revest@...omium.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, bpf <bpf@...r.kernel.org>, Sven
 Schnelle <svens@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>, Jiri
 Olsa <jolsa@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Daniel
 Borkmann <daniel@...earbox.net>, Alan Maguire <alan.maguire@...cle.com>,
 Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner
 <tglx@...utronix.de>, Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH v3 00/27] function_graph: Allow multiple users for
 function graph tracing

On Tue, 4 Jun 2024 18:04:22 +0100
Mark Rutland <mark.rutland@....com> wrote:

> > There may have been something arch specific that I'm unaware about. I'll
> > look at that deeper.  
> 
> It looks like e are lines in the trace that it doesn't expect:
> 
> 	+ cat trace
> 	+ grep -v ^#
> 	+ grep 970
> 	+ wc -l
> 	+ count_pid=0
> 	+ cat trace
> 	+ grep -v ^#
> 	+ grep -v 970
> 	+ wc -l
> 	+ count_other=3
> 	+ [ 0 -eq 0 -o 3 -ne 0 ]
> 	+ fail PID filtering not working?
> 
> ... where we expect that count_other to be 0.
> 
> I hacked in a 'cat trace' just before the 'fail' and that shows:
> 
> 	+ cat trace
> 	# tracer: function_graph
> 	#
> 	# CPU  DURATION                  FUNCTION CALLS
> 	# |     |   |                     |   |   |   |
> 	 3) ! 143.685 us  |  kernel_clone();
> 	 3) ! 127.055 us  |  kernel_clone();
> 	 1) ! 127.170 us  |  kernel_clone();
> 	 3) ! 126.840 us  |  kernel_clone();
> 
> I'm not sure if that's legitimate output the test is failing to account
> for or if that indicates a kernel-side issue.

Bah, I just ran the test.d/ftrace/func-filter-pid.tc and it fails too. This
did pass my other tests that do run ftracetests. Hmm, I just ran it on my
test box that does the tests and it passes there. I wonder if there's some
config option that makes it fail :-/

Well, now that I see it fail, I can investigate.

-- Steve