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Message-ID: <871rgtyz9g.fsf@nanos.tec.linutronix.de>
Date: Mon, 16 Nov 2020 18:42:19 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>
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 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 ...
Thanks,
tglx
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