linux-kernel - Re: [PATCH] tracing: use ring_buffer_record_is_set_on() in tracer_tracing_is

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Date: Mon, 12 Feb 2024 23:54:00 +0100
From: Mete Durlu <meted@...ux.ibm.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Sven Schnelle <svens@...ux.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: use ring_buffer_record_is_set_on() in
 tracer_tracing_is_on()

On 2/12/24 19:53, Steven Rostedt wrote:
> 
> Right, it will definitely force the race window to go away.
> 
> Can you still trigger this issue with just Sven's patch and not this change?
Sven's patch makes the test cases much more resilient. I needed to ramp
up the load up to 4 stressors on a 4 core system before the test starts
to fail again. At this point it is fair to say that the system is under
significant load.

The failing condition is now different, which tells me that
Sven's patch have already solved(or improved) the previous issue.
What is failing now:

   echo '** ENABLE TRACING'
   enable_tracing

   cnt=`cnt_trace`
   if [ $cnt -eq 0 ]; then
      fail "Nothing found in trace"
   fi

Adding a sleep between enable_tracing and cnt_trace seems to improve the
situation a lot. (my guess is that, the trace writer isn't getting any
runtime before the test checks the trace output)

   echo '** ENABLE TRACING'
   enable_tracing

  +sleep $SLEEP_TIME
   cnt=`cnt_trace`
   if [ $cnt -eq 0 ]; then
      fail "Nothing found in trace"
   fi

Didn't see any failure while increasing the system load until 8
stressors (this might have been luck). When system was under load with
8 stressors, I have seen the test failing 2 out of 10 times. Definitely
an improvement over the current situation.