I agree that the reason an interrupt can not sleep is because an interrupt is not associated with any context. But I do not agree that it is specifically because the scheduler can not *resume* the context. In early version, the ISR always borrow the stack of the currently running process, so if the kernel design had allowed ISR sleep, it would automatically be able to implement the context switch naturally. But ISR sleep has been forbidden from the very beginning. The reason why kernel design does not allow ISR sleep is because a process should not be forced to wait for a event that irrelative to itself. When an exception handler sleep, the event it sleeps on is always in some sense related to the process incurring that exception. But if an ISR was allowed to sleep, the event it sleeps on would have nothing to do with the process being interrupted. So my understanding is, the forbidden of ISR sleep is not because of the difficulty to resume context, but because a process should not wait for irrelative event. 2007/5/14, Bahadir Balban <bahadir.balban@xxxxxxxxx>:
On 5/14/07, Learning Linux <learninglinux4@xxxxxxxxx> wrote: > Ok, but how about an ISR, that does not take any locks? Why can't we > sleep in SUCH an ISR? > LL > - The killer reason why you can't sleep in an interrupt is because an interrupt is not associated with any context in the first place. What is a context, then? It is the state information for a process. This includes the kernel and userspace stack pointers, the register set, and the page tables for that process. The scheduler has access to all this information, to preempt one process and run another. Contrary to this, an interrupt, depending on the version of your kernel and arch, uses a separate irq stack or the kernel stack of the interrupted process. An irq is not a context but merely a temporary execution to be concluded asap. Hope this helps, Bahadir -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
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