s390/wti: Prepare graceful CPU pre-emption on wti reception
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.
projects / users / jedix / linux-maple.git / commit