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Date:   Tue, 13 Aug 2019 11:53:06 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Paul Thomas <pthomas8589@gmail.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        dunc.mcphie@gmail.com, Anders Roxell <anders.roxell@linaro.org>
Subject: Re: poor cyclictest results with 5.0 series rt for arm64
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On 2019-07-17 18:28:51 [-0400], Paul Thomas wrote:
> On Wed, Jul 17, 2019 at 6:21 AM Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > On Wed, 17 Jul 2019, Thomas Gleixner wrote:
> > > On Wed, 17 Jul 2019, Thomas Gleixner wrote:
> > >
> > > The one below should fix it for real.
> >
> > That still has an issue which needs deeper investigation. Just keep the
> > offending patch reverted for now.
> 
> OK, sounds good.

could you please try the following hunk?

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 6808cd9526c67..63c6960262861 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -648,7 +648,8 @@ alternative_if ARM64_HAS_IRQ_PRIO_MASKING
 	orr	x24, x24, x0
 alternative_else_nop_endif
 
-	cbnz	x24, 2f					// preempt count != 0
+	cbz	x24, 1f					// (need_resched + count) == 0
+	cbnz	w24, 2f					// count != 0
 
 	ldr	w24, [tsk, #TSK_TI_PREEMPT_LAZY]	// get preempt lazy count
 	cbnz	w24, 2f					// preempt lazy count != 0

> -Paul

Sebastian