On Thursday 24 October 2002 12:24 am, Anjaneyulu wrote: > Hi, > I have a doubt about the interrupt handling and the scheduling. > When an ISR is being executed, that particular interrupt is disable. > Suppose the ISR is waking up a process using wake_up_process(). > Before that particular process is able to execute any statement, if another > interrupt comes and hence ISR will again execute. > > My question is if the interrupts are coming at very high frequency, the > process will never get the chance to execute. Is it right??? > > Please tell me the scheduler reaction to an interrupt. What happens to the > current process???? > On Thursday 24 October 2002 12:24 am, you wrote: > Hi, > I have a doubt about the interrupt handling and the scheduling. > When an ISR is being executed, that particular interrupt is disable. > Suppose the ISR is waking up a process using wake_up_process(). > Before that particular process is able to execute any statement, if another > interrupt comes and hence ISR will again execute. > > My question is if the interrupts are coming at very high frequency, the > process will never get the chance to execute. Is it right??? > > Please tell me the scheduler reaction to an interrupt. What happens to the > current process???? > If there is only one cpu, you are right. If interrupts happened at a high enough frequency, they could stop the current process from executing anything at all because the ISR cannot share the same CPU with the current process. That is why interrupts MUST return quickly. Any interrupt processing that can be deferred until later should be executed in "soft-irqs" and "bottom-halves" at a later time. Soft-Irqs and bottom-halves are ways of scheduling non-essential interrupt processing to happen at a later time. Secondly, a process woken up by a ISR will never be scheduled to run until the ISR returns. Therefore, calling wake_up_process() has no effect other than to place the sleeping process back onto the run queue (the list of runnable processes) and set the reschedule bit that reminds the OS that it needs to call schedule() as soon as possible. When the ISR exits, the OS will call schedule(). Anton > Thanks in advance. > > Regards, > Anj > Thanks in advance. > > Regards, > Anj -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
