From 260252300d2d37c75dd1f3828d29e515f6626b80 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 8 Jul 2015 17:14:48 +0200 Subject: [PATCH 39/64] arm: Disable jump-label on PREEMPT_RT. Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.82-rt27.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 Signed-off-by: Sebastian Andrzej Siewior Link: https://lkml.kernel.org/r/20220613182447.112191-2-bigeasy@linutronix.de --- arch/arm/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 717e596dc13b..f170f29e98ac 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -71,7 +71,7 @@ config ARM select HARDIRQS_SW_RESEND 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 -- 2.44.0