linux-kernel - Re: [patch 10/19] preempt: Cleanup the macro maze a bit

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Message-ID: <20201116121748.GD3121378@hirez.programming.kicks-ass.net>
Date:   Mon, 16 Nov 2020 13:17:48 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paul McKenney <paulmck@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        linux-um@...ts.infradead.org, Russell King <linux@...linux.org.uk>,
        Marc Zyngier <maz@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch 10/19] preempt: Cleanup the macro maze a bit

On Fri, Nov 13, 2020 at 03:02:17PM +0100, Thomas Gleixner wrote:

> -#define irq_count()	(preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
> -				 | NMI_MASK))
> +#define irq_count()	(nmi_count() | hardirq_count() | softirq_count())


> +#define in_task()		(!(in_nmi() | in_hardirq() | in_serving_softirq()))
> -#define in_task()		(!(preempt_count() & \
> -				   (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))

How horrible is the code-gen? Because preempt_count() is
raw_cpu_read_4() and at least some old compilers will refuse to CSE it
(consider the this_cpu_read_stable mess).