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From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 8 Jul 2015 17:14:48 +0200
Subject: [PATCH 1/2] arm: Disable jump-label on PREEMPT_RT.
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
jump-labels are used to efficiently switch between two possible code
paths. To achieve this, stop_machine() is used to keep the CPU in a
known state while the opcode is modified. The usage of stop_machine()
here leads to large latency spikes which can be observed on PREEMPT_RT.
Jump labels may change the target during runtime and are not restricted
to debug or "configuration/ setup" part of a PREEMPT_RT system where
high latencies could be defined as acceptable.
Disable jump-label support on a PREEMPT_RT system.
[bigeasy: Patch description.]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/20220613182447.112191-2-bigeasy@linutronix.de
---
arch/arm/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -73,7 +73,7 @@ config ARM
select HAS_IOPORT
select HAVE_ARCH_AUDITSYSCALL if AEABI && !OABI_COMPAT
select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
- select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
+ select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU && !PREEMPT_RT
select HAVE_ARCH_KFENCE if MMU && !XIP_KERNEL
select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
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