linux-kernel - Re: [patch V4 part 1 07/36] locking/atomics: Flip fallbacks and instrumentation

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Date:   Tue, 5 May 2020 17:04:22 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V4 part 1 07/36] locking/atomics: Flip fallbacks and
 instrumentation

On Tue, May 05, 2020 at 03:16:09PM +0200, Thomas Gleixner wrote:
> Currently instrumentation of atomic primitives is done at the
> architecture level, while composites or fallbacks are provided at the
> generic level.
> 
> The result is that there are no uninstrumented variants of the
> fallbacks. Since there is now need of such (see the next patch),
> invert this ordering.
> 
> Doing this means moving the instrumentation into the generic code as
> well as having (for now) two variants of the fallbacks.
> 
> Notes:
> 
>  - the various *cond_read* primitives are not proper fallbacks
>    and got moved into linux/atomic.c. No arch_ variants are
>    generated because the base primitives smp_cond_load*()
>    are instrumented.
> 
>  - once all architectures are moved over to arch_atomic_ we can remove
>    one of the fallback variants and reclaim some 2300 lines.
> 
>  - atomic_{read,set}*() are no longer double-instrumented
> 
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Mark Rutland <mark.rutland@....com>

FWIW, the scripting changes all look fine to me, so:

Acked-by: Mark Rutland <mark.rutland@....com>

I'm hoping that I can convert the remaining arches over to arch_atomic
atop of this, at which point we can remove the duplication, and have the
usual arch_<foo>/raw_<foo>/<foo> split.

Thanks,
Mark.