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256d97d358
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. On 64-bit Arm, it is possible to use jump labels without the stop_machine() call, which architecturally provides a way to atomically change one 32-bit instruction word while keeping maintaining consistency, but this is not generally the case on 32-bit, in particular in thumb2 mode. Disable jump-label support on a PREEMPT_RT system when SMP is enabled. [bigeasy: Patch description.] [arnd: add !SMP case, extend changelog] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Acked-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Linus Walleij <linus.walleij@linaro.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.