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SubjectRe: [patch] enabling APIC and NMI watchdog on UP systems

On Fri, 29 Sep 2000, Keir Fraser wrote:

> Thanks for the info: I'd entirely forgotten about the inter-APIC comms
> bus. That given, I have no problem with clearing the perfctr before
> use. The NMI oopser has saved my bacon on more than one occasion :)

i'm glad to hear that :-) If you have an SMP system then i agree we should
not touch the performance counter at all - i only did it my patch to give
it some testing.

that having all said, i'm not against a generic, nonpriviledged (kernel
based) performance counter API within the kernel (if there is demand), and
such an API should of course have close control over the contents of the
performance counter registers, and in this case the NMI oopser has to
cooperate. Something like doing per-process performance monitoring and
potentially switching the MSRs on task-switch. But as far as i've seen,
most people who want to have that kind of finegrained information about
their system have no problem doing these things as root, and this is a
much simpler implementation.

Ingo

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