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When a warning track interrupt is received, the kernel has only a very limited amount of time to make sure, that the CPU can be yielded as gracefully as possible before being pre-empted by the hypervisor. The interrupt handler for the wti therefore unparks a kernel thread which has being created on boot re-using the CPU hotplug kernel thread infrastructure. These threads exist per CPU and are assigned the highest possible real-time priority. This makes sure, that said threads will execute as soon as possible as the scheduler should pre-empt any other running user tasks to run the real-time thread. Furthermore, the interrupt handler disables all I/O interrupts to prevent additional interrupt processing on the soon-preempted CPU. Interrupt handlers are likely to take kernel locks, which in the worst case, will be kept while the interrupt handler is pre-empted from itself underlying physical CPU. In that case, all tasks or interrupt handlers on other CPUs would have to wait for the pre-empted CPU being dispatched again. By preventing further interrupt processing, this risk is minimized. Once the CPU gets dispatched again, the real-time kernel thread regains control, reenables interrupts and parks itself again. Acked-by: Heiko Carstens <hca@linux.ibm.com> Reviewed-by: Mete Durlu <meted@linux.ibm.com> Signed-off-by: Tobias Huschle <huschle@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
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.