linux-kernel - Re: [PATCH v4 2/4] ftrace: Add support for function argument to graph tracer

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Message-ID: <20250411131254.3e6155ea@gandalf.local.home>
Date: Fri, 11 Apr 2025 13:12:54 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mark Brown <broonie@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Sven Schnelle
 <svens@...ux.ibm.com>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer
 Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Guo Ren
 <guoren@...nel.org>, Donglin Peng <dolinux.peng@...il.com>, Zheng Yejian
 <zhengyejian@...weicloud.com>, Aishwarya.TCV@....com
Subject: Re: [PATCH v4 2/4] ftrace: Add support for function argument to
 graph tracer

On Fri, 11 Apr 2025 17:58:32 +0100
Mark Brown <broonie@...nel.org> wrote:

> On Fri, Apr 11, 2025 at 12:45:52PM -0400, Steven Rostedt wrote:
> > Mark Brown <broonie@...nel.org> wrote:  
> > > On Thu, Apr 10, 2025 at 01:17:45PM -0400, Steven Rostedt wrote:  
> 
> > > > Hmm, I wonder if there's junk being added into the trace.    
> 
> > > > Can you add this patch, and show me the output when it fails again?    
> 
> > Can you show the information before this output, to see what it is actually
> > testing?  
> 
> Here's a bit more of the context - this is literally just the ftrace
> selftests so it'll be doing whatever that does, there's a huge amount of
> log splat generated when enumerating all the triggers.  I do note that
> it appears to assume there's a ping binary which might confusing things,
> though I'm surprised that'd be a regression rather than something that
> just never worked:

Thanks, even though I figured it out...

> # # + yield
> # # + ping 127.0.0.1 -c 1
> # # ./ftracetest: 179: /opt/kselftest/ftrace/test.d/ftrace/func-filter-pid.tc: ping: not found

The ping was just a way to add some extra noise, as sometimes, the system
just went totally idle, and nothing else showed up.

> # # + sleep .001
> # # + cat trace
> # # + grep -v ^#
> # # + grep 5190
> # # + wc -l
> # # + count_pid=2
> # # + cat trace
> # # + grep -v ^#
> # # + grep -v 5190
> # # + wc -l
> # # + count_other=3

This is what I was looking for. The "count_other" is the number of lines of
output that wasn't due to a '#' or something with '5190'.

> # # + [ 2 -eq 0 -o 3 -ne 0 ]

And it was expecting zero.

> # # + cat trace
> # # # tracer: function_graph
> # # #
> # # # CPU  TASK/PID         DURATION                  FUNCTION CALLS
> # # # |     |    |           |   |                     |   |   |   |
> # # 0)  ftracet-5190  | ! 537.633 us  |  kernel_clone(); /* ret=0x1470 */
> # # 
> # # 0)  ftracet-5190  | ! 508.253 us  |  kernel_clone(); /* ret=0x1471 */
> # # 
> # # 0)  ftracet-5190  | ! 215.716 us  |  kernel_clone(); /* ret=0x1476 */
> # # 
> # # 0)  ftracet-5190  | ! 493.890 us  |  kernel_clone(); /* ret=0x147b */

But it found 3 blank lines!

> That'll take a bit more arranging, I'm running these tests as batch jobs
> in CI infrastructure.  I'll try to have a look.  The only other test
> that actually failed was:
> 
> # not ok 25 Checking dynamic events limitations
> 
> which isn't flagged as a regression (there's some other UNRESOLVED ones).

Hmm, don't know about that one.

-- Steve