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Date: Tue, 17 Nov 2020 11:21:19 +0100
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch 10/19] preempt: Cleanup the macro maze a bit
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>, Rich Felker <dalias@libc.org>, Catalin Marinas <catalin.marinas@arm.com>, Paul McKenney <paulmck@kernel.org>, Arnd Bergmann <arnd@arndb.de>, linux-sh@vger.kernel.org, Richard Weinberger <richard@nod.at>, Frederic Weisbecker <frederic@kernel.org>, Valentin Schneider <valentin.schneider@arm.com>, Jeff Dike <jdike@addtoit.com>, LKML <linux-kernel@vger.kernel.org>, Yoshinori Sato <ysato@users.sourceforge.jp>, "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>, linux-parisc@vger.kernel.org, Helge Deller <deller@gmx.de>, Russell King <linux@armlinux.org.uk>, linux-um@lists.infradead.org, Will Deacon <will@kernel.org>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, linux-arm-kernel@lists.infradead.org, Anton Ivanov <anton.ivanov@cambridgegreys.com>

On Mon, Nov 16, 2020 at 06:42:19PM +0100, Thomas Gleixner wrote:
> On Mon, Nov 16 2020 at 13:17, Peter Zijlstra wrote:
> > 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).
> 
> I looked at gcc8 and 10 output and the compilers are smart enough to
> fold it for the !RT case. But yeah ...

If recent GCC is smart enough I suppose it doesn't matter, thanks!

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