On Fri, 1 Aug 2003, Senthil Kumar R wrote: > Hi, > If my task P is currently executing in the CPU and if an interrupt occurs during that time, I understand that there will be a context switch and the interrupt service routine will be executed in the Kernel's context. > > Once the interrupt service routine is over, > will my task P gets to the CPU > (Assuming P has its time slice yet to finish) > or > will the scheduler take control? My understanding is as follows: Depends. The need_schedule flag of the process will be checked. If set , the scheduler is called. If not set, the current process is continued. Lets follow the code. in /include/asm/hw_irq.h interrupt handlers are registered with these. there are various macros (starting with BUILD_) An important one is BUILD_COMMON_IRQ that calls do_irq that eventually jumps to ret_from_intr. ret_from_intr is a label in arch/i386/kernel/entry.S which tests if the process is returning to user-mode or virtual-86 mode. If so, it jumps to jmp_with_reschedule which tests the need_reschedule flag in the task_struct. if this is a kernel process that was interrupted, scheduler is not called (jmp to ret_with_reschedule is not made and kernel chugs along. Specifically, if the process has time slice left , it should continue merrily. Hope this help. Somebody, please correct me if I was wrong. Thanks. Vijay Subramanian -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
