Messages in this thread | | | Subject | Re: [PATCH v2 1/2] sched/wait: Add add_wait_queue_priority() | From | Paolo Bonzini <> | Date | Wed, 4 Nov 2020 12:25:27 +0100 |
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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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