On Thursday, June 11, 2015 04:50:52 PM Stefan Andritoiu wrote: > Hello, > > From the FreeBSD Handbook: "FreeBSD deals with interrupt handlers by > giving them their own thread context". > From my understanding when a IPI is received the thread that will run > it is placed on the real-time runq, and the scheduler will be invoked > to schedule it. > > So the sequence should be: > currently running thread -> scheduler thread -> interrupt handler -> > scheduler thread -> previously interrupted thread (if no thread > priority change took place inside the interrupt handler) > > Is this correct?
(Sorry these replies are dated.) IPIs do not run in a dedicated thread. Only device interrupt handlers run in a dedicated thread. IPIs (and some device handlers such as timer interrupts) borrow the stack of the currently executing thread to run their handler. As a result, you should have no context switches when an IPI is received unless the IPI handler specifically invokes one. One IPI that explicitly swithes is IPI_PREEMPT. However, other IPIs can result in a switch if the interrupted thread is running in userland and a context switch to another thread is performed via the checks in userret() and/or ast(). This is how IPI_AST is used. It has a NULL handler and is only sent to trigger the side effects in userret() in case the thread is executing in userland. -- John Baldwin _______________________________________________ freebsd-virtualization@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-virtualization To unsubscribe, send any mail to "freebsd-virtualization-unsubscr...@freebsd.org"
