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--- realtime:documentation:threadirq [2016/06/23 08:22]
anna-maria created
+++ — (current)
@@ Line 1: / Line 1: @@
-====== Threaded interrupt handler ======
-In mainline Linux the interrupt service routine is processed in hard
-interrupt context with hardware interrupts disabled.  Hardware
-interrupts disabled implies that preemption and soft interrupts are
-also disabled.  Interrupt handlers are processed in context of the
-interrupt service routine with hard interrupts disabled as well.  The
-kernel command line option `threadirqs` changes the the interrupt
-handlers to run in a threaded context.  The scheduler policy of the
-thread is set to SCHED_FIFO with a default priority of 50.
-All interrupt handlers marked with the IRQF_NO_THREAD flag will not be
-threaded and run with hard interrupts disabled.  This flag is used for
-example by Inter-Processor Interrupts (IPIs).  Interrupt handlers set
-up with the IRQF_TIMER or IRQF_PER_CPU flag are marked as
-IRQF_NO_THREAD implicitly.
-The PREEMPT_RT patch forces the `threadirqs` command line option.
-There is a small difference between the behavior of threaded
-interrupts in the mainline and PREEMPT_RT implementations, illustrated
-in the following table:
-<WRAP center 400px>
-|                                ^ Mainline ^ PREEMPT_RT |
-^hard interrupts disabled        |          |            |
-^soft interrupts disabled        | ✓        | ✓          |
-^preemption disabled             | ✓        |            |
-</WRAP>

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