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    SubjectRe: [PATCH v2 1/2] sched/wait: Add add_wait_queue_priority()
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    On 04/11/20 10:35, David Woodhouse wrote:
    > On Wed, 2020-10-28 at 15:35 +0100, Peter Zijlstra wrote:
    >> On Tue, Oct 27, 2020 at 02:39:43PM +0000, David Woodhouse wrote:
    >>> From: David Woodhouse <dwmw@amazon.co.uk>
    >>>
    >>> This allows an exclusive wait_queue_entry to be added at the head of the
    >>> queue, instead of the tail as normal. Thus, it gets to consume events
    >>> first without allowing non-exclusive waiters to be woken at all.
    >>>
    >>> The (first) intended use is for KVM IRQFD, which currently has
    >>> inconsistent behaviour depending on whether posted interrupts are
    >>> available or not. If they are, KVM will bypass the eventfd completely
    >>> and deliver interrupts directly to the appropriate vCPU. If not, events
    >>> are delivered through the eventfd and userspace will receive them when
    >>> polling on the eventfd.
    >>>
    >>> By using add_wait_queue_priority(), KVM will be able to consistently
    >>> consume events within the kernel without accidentally exposing them
    >>> to userspace when they're supposed to be bypassed. This, in turn, means
    >>> that userspace doesn't have to jump through hoops to avoid listening
    >>> on the erroneously noisy eventfd and injecting duplicate interrupts.
    >>>
    >>> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
    >>
    >> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    >
    > Thanks. Paolo, the conclusion was that you were going to take this set
    > through the KVM tree, wasn't it?
    >

    Yes.

    Paolo

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