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 18:12:02 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Mete Durlu <meted@...ux.ibm.com>
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 Mon, 12 Feb 2024 23:54:00 +0100
Mete Durlu <meted@...ux.ibm.com> wrote:

> 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.
> 


So, I plan on adding Sven's patch for my next pull request to Linus. I had
forgotten it when I did my last one (largely due to traveling). I'll hold
off a week to see if any other fixes come in.

-- Steve