From:   Valentin Schneider <valentin.schneider@arm.com>
To:     Mike Galbraith <efault@gmx.de>, Marco Elver <elver@google.com>
Cc:     linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
        linuxppc-dev@lists.ozlabs.org, linux-kbuild@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH v2 2/5] preempt/dynamic: Introduce preempt mode accessors
In-Reply-To: <26fd47db11763a9c79662a66eed2dbdbcbedaa8a.camel@gmx.de>
References: <20211110202448.4054153-1-valentin.schneider@arm.com> <20211110202448.4054153-3-valentin.schneider@arm.com> <a7c704c2ae77e430d7f0657c5db664f877263830.camel@gmx.de> <803a905890530ea1b86db6ac45bd1fd940cf0ac3.camel@gmx.de> <a7febd8825a2ab99bd1999664c6d4aa618b49442.camel@gmx.de> <CANpmjNPeRwupeg=S8yGGUracoehSUbS-Fkfb8juv5mYN36uiqg@mail.gmail.com> <26fd47db11763a9c79662a66eed2dbdbcbedaa8a.camel@gmx.de>
Date:   Thu, 11 Nov 2021 10:56:20 +0000
Message-ID: <8735o3rmej.mognet@arm.com>
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On 11/11/21 11:32, Mike Galbraith wrote:
> On Thu, 2021-11-11 at 10:36 +0100, Marco Elver wrote:
>> I guess the question is if is_preempt_full() should be true also if
>> is_preempt_rt() is true?
>
> That's what CONFIG_PREEMPTION is.  More could follow, but it was added
> to allow multiple models to say "preemptible".
>

That's what I was gonna say, but you can have CONFIG_PREEMPTION while being
is_preempt_none() due to PREEMPT_DYNAMIC...

>> Not sure all cases are happy with that, e.g. the kernel/trace/trace.c
>> case, which wants to print the precise preemption level.
>
> Yeah, that's the "annoying" bit, needing one oddball model accessor
> that isn't about a particular model.
>
>> To avoid confusion, I'd introduce another helper that says true if the
>> preemption level is "at least full", currently that'd be "full or rt".
>> Something like is_preempt_full_or_rt() (but might as well write
>> "is_preempt_full() || is_preempt_rt()"), or is_preemption() (to match
>> that Kconfig variable, although it's slightly confusing). The
>> implementation of that helper can just be a static inline function
>> returning "is_preempt_full() || is_preempt_rt()".
>>
>> Would that help?
>
> Yeah, as it sits two accessors are needed, one that says PREEMPT the
> other PREEMPTION, spelling optional.
>

Per the above, I think we need the full || rt thingie.

>       -Mike