linux-kernel - Re: [PATCH] selftests/ftrace: Do not trace do_softirq because of PREEMPT

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Date:   Thu, 10 Feb 2022 00:00:03 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Shuah Khan <shuah@...nel.org>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, joseph.salisbury@...onical.com
Subject: Re: [PATCH] selftests/ftrace: Do not trace do_softirq because of
 PREEMPT_RT

On Wed,  9 Feb 2022 17:24:30 +0100
Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com> wrote:

> The PREEMPT_RT patchset does not use soft IRQs thus trying to filter for
> do_softirq fails for such kernel:
> 
>   echo do_softirq
>   ftracetest: 81: echo: echo: I/O error
> 
> Choose some other externally visible function for the test.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
> 
> ---
> 
> I understand that the failure does not exist on mainline kernel (only
> with PREEMPT_RT patchset) but the change does not harm it.
> 
> If it is not suitable alone, please consider it for RT patchset.
> ---
>  .../selftests/ftrace/test.d/ftrace/func_set_ftrace_file.tc      | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func_set_ftrace_file.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func_set_ftrace_file.tc
> index e96e279e0533..1d0c7601865f 100644
> --- a/tools/testing/selftests/ftrace/test.d/ftrace/func_set_ftrace_file.tc
> +++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_set_ftrace_file.tc
> @@ -19,7 +19,7 @@ fail() { # mesg
>  
>  FILTER=set_ftrace_filter
>  FUNC1="schedule"
> -FUNC2="do_softirq"
> +FUNC2="_printk"

The problem with the above, is that it is not guaranteed to trigger (and
probably will not), where as the do_softirq is. The filtering is suppose to
trace something that actually happens.

How about using: scheduler_tick ?

-- Steve


>  
>  ALL_FUNCS="#### all functions enabled ####"
>