Re: [patch] preemptive kernel

From: ludovic fernandez (ludovic.fernandez@sun.com)
Date: Mon Aug 14 2000 - 15:33:07 EST


Hello,

Pavel Machek wrote:

> Hi!
>
> > The following patch make the system preemptable; a task
> > (kernel or user) can be scheduled while running in the
> > kernel space if this is safe to do so.
> > The results are quite interesting.
> > The patch is against 2.2.16 and is for UP only on intel platforms.
>
> This looks nicely. Perhaps it should be config option, and it better
> should be against 2.4.0, but it is nice. [This seems to follow Linus'
> solution pretty closely, does it?]
> Pavel
> --

I agree. I don't think the patch changes dramatically the
system in 2.2 because the kernel is pretty damn locked.
Some [few] people told me that the patch was improving the
response time of the system but I believe it's only improving
specific paths.
2.4 seems to use a more fine grain locking mechanism, so maybe
it's worth trying it...
Personally, I believe that the advantage of having a preemptive
kernel is not [to try] to improve the response time of user tasks
but rather to ease the support of kernel threads. The notion of
modules in Linux is nice. When you add the possibility to have
threads inside your module, the functionality becomes VERY nice.
Right now, when a guy decides to add a kernel thread, he also needs
to put preemption points in his thread. The only way he can do that
is based on what the thread is doing (in terms of instructions executed),
which is [I think] wrong; the scheduling should be done based on
the time it takes to do it.

Any comments ?

Ludo.

PS: I'd like to add that this patch has nothing to do with real time.

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