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    SubjectRe: [PATCH 2/11] oprofile: arch-independent code for stack trace sampling
    On Tue, Nov 09, 2004 at 10:35:48PM +1100, Greg Banks wrote:

    > > oprofile is currently doing suspicious things with smp_processor_id() in
    > > premptible reasons. Is this patch compounding things?
    >
    > It's not changing the contexts where smp_processor_id() is called,
    > just pushing it down one level from a bunch of interrupt handlers
    > to the 2 oprofile sampling functions they call. If it was busted
    > before it's no more nor less busted now.
    >
    > I presume the perceived problem is that with CONFIG_PREEMPT=y the
    > thread can be pre-empted onto another CPU? If it makes everyone
    > happier I can sprinkle a few preempt_disable()s around, but I'd
    > prefer to do it in a subsequent patch rather than respin this.

    Andrew: basically the warning is false, there is no bug in this code.

    we don't want to use preempt_disable(). Instead we want some way to get
    a CPU ID and then carry on in pre-emptible fashion. It's only used to
    index into an array, and if we get pre-empted onto another CPU it's not
    a major deal.

    (Yes, this breaks with CPU hotplug, but so does the rest of OProfile and
    I've yet to see a sensible API for handling this, that is a ctor/dtor
    style API)

    regards
    john
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