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Date:   Thu, 10 Feb 2022 15:10:44 +0100
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From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>, Shuah Khan <shuah@kernel.org>,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-rt-users@vger.kernel.org, joseph.salisbury@canonical.com,
        Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH v2] selftests/ftrace: Do not trace do_softirq because of
 PREEMPT_RT
Message-ID: <YgUc5HxfIdJ0Z5AN@linutronix.de>
References: <20220210083356.11212-1-krzysztof.kozlowski@canonical.com>
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 <546f147d-1682-fb92-42e5-7247dc19dcf1@canonical.com>
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On 2022-02-10 15:05:24 [+0100], Krzysztof Kozlowski wrote:
> On 10/02/2022 14:47, Sebastian Andrzej Siewior wrote:
> > 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.
> 
> Correct. It does not use do_softirq() code, but follows different path
> with ksoftirqd.
> Shall I rephrase it towards something like this? Or maybe you have some
> more accurate description?

It would be good to describe what the purpose of the change in terms of
the actual problem and the aimed solution.

> The implementation detail is that do_softirq() is in ifndef.

So let me ask again.  We have
   FUNC1="schedule"
   FUNC2="do_softirq"

What is the purpose of this? Do you need FUNC2 when ksoftirqd is run or
when softirqs are served? Not sure how scheduler_tick fits in all this.

> Best regards,
> Krzysztof

Sebastian