On Fri, 6 Nov 2020 11:17:21 +0100 Paolo Bonzini <pbonzini@xxxxxxxxxx> 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@xxxxxxxxxxxx> > >>> > >>> 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@xxxxxxxxxxxx> > >> > >> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > > > > 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, Alex
