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    SubjectRe: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi
    On Tue, 5 Jun 2012, Andi Kleen wrote:
    > Thomas Gleixner <> writes:
    > >
    > > Vs. the interrupt/timer/other crap madness:
    > >
    > > - We really don't want to have an interrupt balancer in the kernel
    > > again, but we need a mechanism to prevent the user space balancer
    > > trainwreck from ruining the power saving party.
    > Why not? I think the kernel is exactly the right place for it.
    > It's essentially a scheduling problem. Scheduling in user space
    > is not a good idea.

    No argument about scheduling in user space. Though the real problem is
    where do you draw the line between mechanism and policy?

    > With MSI-X the drivers just want a static setting. User space
    > shouldn't mess with it.
    > Some of the workarounds for user space messing with it (like that
    > interrupt rmap code) are really bad and just a workaround for doing the
    > scheduling in the wrong place.
    > For dynamic changes it should indeed by part of scheduling,
    > following similar rules, with only high level policy input
    > from userland.

    I'd be happy to see a patch which implements all of that and avoids
    the pitfalls of the old in kernel irq balancer along with the short
    comings of the user space one.



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