linux-kernel - Re: [PATCH v2] selftests/ftrace: Do not trace do_softirq because of PREEMPT

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Date:   Thu, 10 Feb 2022 14:47:28 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        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,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2] selftests/ftrace: Do not trace do_softirq because of
 PREEMPT_RT

On 2022-02-10 09:33:56 [+0100], Krzysztof Kozlowski wrote:
> The PREEMPT_RT patchset does not use soft IRQs thus trying to filter for
> do_softirq fails for such kernel:

PREEMPT_RT does use soft IRQs.

>   echo do_softirq
>   ftracetest: 81: echo: echo: I/O error
> 
> Choose some other visible function for the test.
> 
…

> --- 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="scheduler_tick"

What is the purpose of this?

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

Sebastian