lkml.org 
[lkml]   [2012]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v2 5/6] kvm: KVM_EOIFD, an eventfd for EOIs
    From
    Date
    On Wed, 2012-06-27 at 17:51 +0300, Gleb Natapov wrote:
    > On Wed, Jun 27, 2012 at 08:29:04AM -0600, Alex Williamson wrote:
    > > On Wed, 2012-06-27 at 16:58 +0300, Gleb Natapov wrote:
    > > > On Tue, Jun 26, 2012 at 11:10:08PM -0600, Alex Williamson wrote:
    > > > > This new ioctl enables an eventfd to be triggered when an EOI is
    > > > > written for a specified irqchip pin. By default this is a simple
    > > > > notification, but we can also tie the eoifd to a level irqfd, which
    > > > > enables the irqchip pin to be automatically de-asserted on EOI.
    > > > > This mode is particularly useful for device-assignment applications
    > > > > where the unmask and notify triggers a hardware unmask. The default
    > > > > mode is most applicable to simple notify with no side-effects for
    > > > > userspace usage, such as Qemu.
    > > > >
    > > > > Here we make use of the reference counting of the _irq_source
    > > > > object allowing us to share it with an irqfd and cleanup regardless
    > > > > of the release order.
    > > > >
    > > > > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
    > > > > ---
    > > > >
    > > > > Documentation/virtual/kvm/api.txt | 24 +++++
    > > > > arch/x86/kvm/x86.c | 1
    > > > > include/linux/kvm.h | 14 +++
    > > > > include/linux/kvm_host.h | 13 +++
    > > > > virt/kvm/eventfd.c | 189 +++++++++++++++++++++++++++++++++++++
    > > > > virt/kvm/kvm_main.c | 11 ++
    > > > > 6 files changed, 250 insertions(+), 2 deletions(-)
    > > > >
    > > > > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
    > > > > index b216709..87a2558 100644
    > > > > --- a/Documentation/virtual/kvm/api.txt
    > > > > +++ b/Documentation/virtual/kvm/api.txt
    > > > > @@ -1987,6 +1987,30 @@ interrupts with those injected through KVM_IRQ_LINE. IRQFDs created
    > > > > with KVM_IRQFD_FLAG_LEVEL must also set this flag when de-assiging.
    > > > > KVM_IRQFD_FLAG_LEVEL support is indicated by KVM_CAP_IRQFD_LEVEL.
    > > > >
    > > > > +4.77 KVM_EOIFD
    > > > > +
    > > > > +Capability: KVM_CAP_EOIFD
    > > > > +Architectures: x86
    > > > > +Type: vm ioctl
    > > > > +Parameters: struct kvm_eoifd (in)
    > > > > +Returns: 0 on success, -1 on error
    > > > > +
    > > > > +KVM_EOIFD allows userspace to receive EOI notification through an
    > > > > +eventfd for level triggered irqchip interrupts. Behavior for edge
    > > > > +triggered interrupts is undefined. kvm_eoifd.fd specifies the eventfd
    > > > Lets make it defined. EOI notification can be used by userspace to fix
    > > > time drift due to lost interrupts. But than userspace needs to know
    > > > which vcpu did EOI.
    > >
    > > Hmm, do we need an additional flag and field in kvm_eoifd to filter by
    > > vCPU then?
    > >
    > This will be enough for a use case I am aware of. Don't know if this
    > interface is generic enough for all possible use cases.

    That's generally a hard prediction to make ;) We currently don't pass a
    kvm_vcpu anywhere close to the irq ack notifier. The ioapic path could
    be relatively trivial, but the pic path is a bit further disconnected.
    If we had that plumbing, a KVM_CAP plus vcpu filter flag and specifying
    the vcpu using some of the padding space seems like it's sufficient.
    I'll drop mention of level-only from the description, but the plumbing
    and vcpu filtering can be a follow-on. Thanks,

    Alex



    \
     
     \ /
      Last update: 2012-06-28 06:21    [W:0.025 / U:4.548 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site