linux-kernel - Re: [PATCH] arm64: Avoid pointless schedule_preempt

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Message-ID: <alpine.DEB.2.21.1907171203280.1767@nanos.tec.linutronix.de>
Date:   Wed, 17 Jul 2019 12:04:55 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Valentin Schneider <valentin.schneider@....com>
cc:     LAK <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] arm64: Avoid pointless schedule_preempt_irq()
 invocations

On Wed, 17 Jul 2019, Valentin Schneider wrote:

> On 17/07/2019 09:43, Thomas Gleixner wrote:
> > When preempt_count is zero on return from interrupt then
> > schedule_preempt_irq() is invoked even if TIF_NEED_RESCHED is not set.
> > 
> > That does not make sense because schedule_preempt_irq() has to go through a
> > full __schedule() for nothing in that case.
> > 
> > Check TIF_NEED_RESCHED and invoke schedule_preempt_irq() only if set.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> Don't we have NEED_RESCHED squashed into preempt count?
> 
>   396244692232 ("arm64: preempt: Provide our own implementation of asm/preempt.h")
> 
> So the existing check should cover that, unless I'm missing something?

Right. Ignore me.