linux-kernel - Re: [PATCH v3 06/20] seqlock: Extend seqcount API with associated locks

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Message-ID: <20200708155813.GA147953@debian-buster-darwi.lab.linutronix.de>
Date:   Wed, 8 Jul 2020 17:58:13 +0200
From:   "Ahmed S. Darwish" <a.darwish@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 06/20] seqlock: Extend seqcount API with associated
 locks

On Wed, Jul 08, 2020 at 05:35:22PM +0200, Peter Zijlstra wrote:
...
>
> And while the gcc-4.8 code is horrendous crap, the rest should be pretty
> straight forward and concentrates on the pieces where there are
> differences.
>

Is there any possibility of upgrading the minimum gcc version to 4.9? Is
there any supported architecture that is still stuck on 4.8?

...
> I even considered:
>
> #define __SEQPROP(name, prop, expr) \
> static __always_inline __seqprop_##prop##_t \
> __seqprop##name##_##prop(seqcount##name##_t *s) \
> { \
> 	expr; \
> }
>
> Such that we could write:
>
> __SEQPROP(, ptr, return s)
> __SEQPROP(, preempt, return false)
> __SEQPROP(, assert, )
>
> __SEQPROP(_##locktype, ptr, return &s->seqcount) \
> __SEQPROP(_##locktype, preempt, return preempt) \
> __SEQPROP(_##locktype, assert, __SEQCOUNT_LOCKDEP(lockdep_assert_held(s->lockmember))) \
>
> But I figured _that_ might've been one step too far ;-)

Initially I implemented something like this during internal,
pre-upstream, versions of this patch series. We've decided afterwards
that the macro compression level is so high that the whole thing is not
so easily understandable.

Thanks,

--
Ahmed S. Darwish
Linutronix GmbH