From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-arm-kernel@lists.infradead.org
Cc: Russell King <linux@armlinux.org.uk>,
Arnd Bergmann <arnd@arndb.de>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH 1/2] arm: Disable jump-label on PREEMPT_RT.
Date: Mon, 13 Jun 2022 20:24:46 +0200 [thread overview]
Message-ID: <20220613182447.112191-2-bigeasy@linutronix.de> (raw)
In-Reply-To: <20220613182447.112191-1-bigeasy@linutronix.de>
From: Thomas Gleixner <tglx@linutronix.de>
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>
---
arch/arm/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 7630ba9cb6ccc..2088d9322588e 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
--
2.36.1
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next prev parent reply other threads:[~2022-06-13 18:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-13 18:24 [PATCH 0/2] arm: Disable two features which are not compatible with PREEMPT_RT Sebastian Andrzej Siewior
2022-06-13 18:24 ` Sebastian Andrzej Siewior [this message]
2022-06-13 18:24 ` [PATCH 2/2] arm: Disable softirq stacks on PREEMPT_RT Sebastian Andrzej Siewior
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