Mulyadi, thank you for the detailed explanation. Thus (a) is a source for interrupt latency and (b) actually fixes it. -- Kostya ---------------------------------------- > Date: Thu, 25 Jun 2009 02:26:25 +0700 > Subject: Re: preemption > From: mulyadi.santosa@xxxxxxxxx > To: bkostya@xxxxxxxxxxx > CC: kernelnewbies@xxxxxxxxxxxx > > Hi... > > 2009/6/24 Kostya B : >> >> >> Dear list, >> >> Please help me to analyze the following scenario: >> >> By having a userspace process 'A' executing a system call. >> Hardware interrupt happens. Do you think on exit from interrupt (irq_exit) >> the context switch could take place? > Yes it could, depending on the preemption model you pick...see below.... > >> Let's assume no softirq work is pending. >> >> (a) kernel is not preemptive > > then it would stay in the current kernel code path, which is executing > the syscall on behalf of running task. > >> (b) kernel is preemptive > > What I am quite sure here is, in full preemptive kernel, after > returning from interrupt handling, scheduler is allowed to pick new > task to be executed. So, let's say scheduler has pick new task > according to certain rules, context switch will happen. > > For voluntary preemption, perhaps you need to check the code by your > own. In my point of view, after reading http://lwn.net/Articles/95334/ > (probably not so relevant anymore), I have impression rescheduling > also happen after returning from interrupt handler. > >> (c) with RT patch > > I have no hands on experience about RT patch. Also you need to > specificly define whether you refer to hard or soft RT. > > I think in both RT style, the preemption might happen after returning > from the interrupt. By doing that, scheduler might be able to pick the > job that almost meet its deadline. > > regards, > > Mulyadi. > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > Please read the FAQ at http://kernelnewbies.org/FAQ > _________________________________________________________________ More than messages–check out the rest of the Windows Live™. http://www.microsoft.com/windows/windowslive/ -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
