Re: [PATCH 4/5] ARM: Disable jump-label on PREEMPT_RT.
From: "Arnd Bergmann" <arnd@arndb.de>
Date: 2025-10-30 15:24:48
Also in:
linux-rt-devel
On Wed, Oct 29, 2025, at 16:59, Sebastian Andrzej Siewior wrote:
quoted hunk ↗ jump to hunk
From: Thomas Gleixner <redacted> 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 <redacted> 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 864a14a434b08..99c9b1c320af8 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig@@ -80,7 +80,7 @@ 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
I posted a slightly different version last year, which optimizes the uniprocessor version and has a little more information in the changelog: https://lore.kernel.org/all/20241210160556.2341497-2-arnd@kernel.org/ (local) Arnd