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    SubjectRe: [PATCH v2 1/2] sched/wait: Add add_wait_queue_priority()
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    On 6 November 2020 16:32:00 GMT, Alex Williamson <alex.williamson@redhat.com> wrote:
    >On Fri, 6 Nov 2020 11:17:21 +0100
    >Paolo Bonzini <pbonzini@redhat.com> wrote:
    >
    >> 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?
    >> >
    >>
    >> Queued, except for patch 2/3 in the eventfd series which Alex hasn't
    >> reviewed/acked yet.
    >
    >There was no vfio patch here, nor mention why it got dropped in v2
    >afaict. Thanks,

    That was a different (but related) series. The VFIO one is https://patchwork.kernel.org/project/kvm/patch/20201027135523.646811-3-dwmw2@infradead.org/

    Thanks.

    --
    Sent from my Android device with K-9 Mail. Please excuse my brevity.

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