From: Valentin Schneider <valentin.schneider@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>,
LAK <linux-arm-kernel@lists.infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arm64: Avoid pointless schedule_preempt_irq() invocations
Date: Wed, 17 Jul 2019 10:54:09 +0100 [thread overview]
Message-ID: <e47e8298-af21-64fa-eac3-6fdfbf11c502@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1907171036490.1767@nanos.tec.linutronix.de>
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@linutronix.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?
> ---
> Found while staring at some RT wrecakge in that area.
> ---
> arch/arm64/kernel/entry.S | 4 ++++
> 1 file changed, 4 insertions(+)
>
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -680,6 +680,10 @@ alternative_if ARM64_HAS_IRQ_PRIO_MASKIN
> orr x24, x24, x0
> alternative_else_nop_endif
> cbnz x24, 1f // preempt count != 0 || NMI return path
> +
> + ldr x0, [tsk, #TSK_TI_FLAGS] // get flags
> + tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?
> +
> bl preempt_schedule_irq // irq en/disable is done inside
> 1:
> #endif
>
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next prev parent reply other threads:[~2019-07-17 9:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 8:43 [PATCH] arm64: Avoid pointless schedule_preempt_irq() invocations Thomas Gleixner
2019-07-17 9:54 ` Valentin Schneider [this message]
2019-07-17 10:04 ` Thomas Gleixner
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