Reentrant and preemptive ?

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Hi all.

I've some questions about the Linux kernel.
We say that Linux is reentrant but not preemptive (until 2.6.x). That means that the code can be executed by two "processes" (threads I should say becoz we're in Kernel mode) in the same time but that a process cannot be interrupted by another. Am I rigth here ?:)
But if the kernel is non preemptive and that we're not using multiple processors, this means that multiple "processes" cannot be executed in the same time, no ?
So, if Linux is a pure non preemptive kernel, non reentrance doesn't affect the Kernel (except for SMP)?


Another point is the non preemptivity of the kernel. In the book I'm reading (Undertsand Linux Kernel from Oreilly), they say that interruptiosn can be nested. So, an interruption can interrupt the current "process". So the Linux kernel is "preemptive" ?

Finally, I'd like to know if on preemptive kernel, kernel threads can be interrupted by user processes.

That's all :)


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