linux-kernel - Re: [RFC PATCH 1/3] arm64: entry: Remove unneeded need

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Message-ID: <20190201102154.GB26637@fuggles.cambridge.arm.com>
Date:   Fri, 1 Feb 2019 10:21:54 +0000
From:   Will Deacon <will.deacon@....com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org,
        Julien Thierry <julien.thierry@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Julien Grall <julien.grall@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 1/3] arm64: entry: Remove unneeded need_resched() loop

On Thu, Jan 31, 2019 at 06:23:37PM +0000, Valentin Schneider wrote:
> Since the enabling and disabling of IRQs within preempt_schedule_irq()
> is contained in a need_resched() loop, we don't need the outer arch
> code loop.
> 
> Reported-by: Julien Thierry <julien.thierry@....com>
> Reported-by: Will Deacon <will.deacon@....com>
> Signed-off-by: Valentin Schneider <valentin.schneider@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Julien Grall <julien.grall@....com>
> Cc: Julien Thierry <julien.thierry@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-arm-kernel@...ts.infradead.org
> ---
>  arch/arm64/kernel/entry.S | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 0ec0c46b2c0c..4d0c81f29a60 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -611,7 +611,7 @@ el1_irq:
>  #ifdef CONFIG_PREEMPT
>  	ldr	x24, [tsk, #TSK_TI_PREEMPT]	// get preempt count
>  	cbnz	x24, 1f				// preempt count != 0
> -	bl	el1_preempt
> +	bl	preempt_schedule_irq		// irq en/disable is done inside
>  1:
>  #endif
>  #ifdef CONFIG_TRACE_IRQFLAGS
> @@ -620,15 +620,6 @@ el1_irq:
>  	kernel_exit 1
>  ENDPROC(el1_irq)
>  
> -#ifdef CONFIG_PREEMPT
> -el1_preempt:
> -	mov	x24, lr
> -1:	bl	preempt_schedule_irq		// irq en/disable is done inside
> -	ldr	x0, [tsk, #TSK_TI_FLAGS]	// get new tasks TI_FLAGS
> -	tbnz	x0, #TIF_NEED_RESCHED, 1b	// needs rescheduling?
> -	ret	x24
> -#endif
> -

Acked-by: Will Deacon <will.deacon@....com>

Catalin can pick this up for 5.1.

Will