Messages in this thread | | | Date | Tue, 29 Feb 2000 14:09:42 +0200 | From | Matti Aarnio <> | Subject | Re: Linux kernerl preemptive ?? |
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On Tue, Feb 29, 2000 at 05:14:46AM +0530, Aneesh Kumar K.V wrote: > Hai , > Can you suggest me some url which discuss all these things . > Actually i didn't get the point . You say kernel is not preemptive but it > can yield to other process when it is waiting for some resources . Well > then why it is not made preemptive . Is SMP used to multiprocessor machine > . Do it have anything to do with preemtion .
Others may have URLs, I don't.
- "SMP" = "Symmetric Multi Processing" (Or in case of Linux: "Symmetric Multi Penguin" -- a joke)
- Pre-emption is a thing where executing thread is involuntarily stopped from doing whatever it was doing, and processor is given to another thread. Linux kernel DOES NOT DO THAT INTERNALLY. Well, there is a sort of hierarchy of pre-emptions: - user threads (+ kernel threads for user syscalls) - scheduling in between user threads - interrupt processing
- Only pre-emption what there is, does happen in between compute- bound user processes when process' timeslice has completed.
- Kernel threads can voluntarily YIELD their processor to other tasks by means of waiting for some resource, or executing explicite schedule() call.
- As to why the kernel isn't made internally pre-emptive; doing such a thing is *difficult*, very difficult.
System would need to be rewritten to allow internal execution stopped at any point, and having other processors/threads trample on incomplete datasets at any point... (Multiprocessor support requires sort of this behaviour anyway, and that is why there are various spinlocks all over the place..)
> regards > aneesh
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