From: Thomas Gleixner <tglx@linutronix.de>
To: 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: [PATCH] arm64: Avoid pointless schedule_preempt_irq() invocations
Date: Wed, 17 Jul 2019 10:43:59 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1907171036490.1767@nanos.tec.linutronix.de> (raw)
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>
---
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 reply other threads:[~2019-07-17 8:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 8:43 Thomas Gleixner [this message]
2019-07-17 9:54 ` [PATCH] arm64: Avoid pointless schedule_preempt_irq() invocations Valentin Schneider
2019-07-17 10:04 ` Thomas Gleixner
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