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 18:04:22 +0100
From: Mark Rutland <mark.rutland@....com>
To: Steven Rostedt <rostedt@...dmis.org>
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, Jun 04, 2024 at 12:31:24PM -0400, Steven Rostedt wrote:
> On Tue, 4 Jun 2024 15:44:40 +0100
> Mark Rutland <mark.rutland@....com> wrote:
> 
> > Hi Steve, Masami,
> > 
> > On Tue, Jun 04, 2024 at 08:18:50AM -0400, Steven Rostedt wrote:
> > > 
> > > Masami,
> > > 
> > > This series passed all my tests, are you comfortable with me pushing
> > > them to linux-next?  
> > 
> > As a heads-up (and not to block pushing this into next), I just gave
> > this a spin on arm64 atop v6.10-rc2, and running the selftests I see:
> > 
> > 	ftrace - function pid filters
> > 	(instance)  ftrace - function pid filters
> > 
> > ... both go from [PASS] to [FAIL].
> > 
> > Everything else looks good -- I'll go dig into why that's happening.
> > 
> > It's possible that's just something odd with the filesystem I'm using
> > (e.g. the wnership test failed because this lacks 'stat').
> 
> Thanks for the update. I could be something I missed in patch 13 that had
> to put back the pid code.
> 
> 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.

Mark.