Preemptible kernel locks
Making the majority of kernel locks preemptible is the most intrusive change that PREEMPT_RT makes and this code remains outside of the mainline kernel.
The problem occurs with spinlocks, which are used for much of the kernel locking. A spinlock is a busy-wait mutex which does not require a context switch in the contended case and so is very efficient as long as the lock is held for a short time. Ideally, they should be locked for less than the time it would take to reschedule twice. The following diagram shows threads running on two different CPUs contending the same spinlock. CPU0 gets it first, forcing CPU1 to spin, waiting until it is unlocked:
The thread that holds the spinlock cannot be preempted since doing so may ...
Get Mastering Embedded Linux Programming now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
