Re: [Qemu-devel] [PATCH 1/2] return available ioeventfds count in kvm_has_many_ioeventfds()

[Amos Kong]

On 13/03/12 19:50, Jan Kiszka wrote:
> Please tag uq/master patches with "PATCH uq/master".
>
> On 2012-03-13 11:42, Amos Kong wrote:
> > Older kernels have a 6 device limit on the KVM io bus.
> > This patch makes kvm_has_many_ioeventfds() return available
> > ioeventfd count. ioeventfd will be disabled if there is
> > no 7 available ioeventfds.
> >
> > Signed-off-by: Amos Kong<address@hidden>
> > ---
> >   hw/virtio-pci.c |    2 +-
> >   kvm-all.c       |    9 +++------
> >   2 files changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> > index a0fb7c1..d63f303 100644
> > --- a/hw/virtio-pci.c
> > +++ b/hw/virtio-pci.c
> > @@ -678,7 +678,7 @@ void virtio_init_pci(VirtIOPCIProxy *proxy, VirtIODevice 
> > *vdev)
> >       pci_register_bar(&proxy->pci_dev, 0, PCI_BASE_ADDRESS_SPACE_IO,
> >                        &proxy->bar);
> >
> > -    if (!kvm_has_many_ioeventfds()) {
> > +    if (kvm_has_many_ioeventfds() != 7) {
> >           proxy->flags&= ~VIRTIO_PCI_FLAG_USE_IOEVENTFD;
> >       }
> >
> > diff --git a/kvm-all.c b/kvm-all.c
> > index 3c6b4f0..d12694b 100644
> > --- a/kvm-all.c
> > +++ b/kvm-all.c
> > @@ -78,7 +78,6 @@ struct KVMState
> >       int pit_in_kernel;
> >       int pit_state2;
> >       int xsave, xcrs;
> > -    int many_ioeventfds;
> >       int irqchip_inject_ioctl;
> >   #ifdef KVM_CAP_IRQ_ROUTING
> >       struct kvm_irq_routing *irq_routes;
> > @@ -510,8 +509,8 @@ static int kvm_check_many_ioeventfds(void)
> >           }
> >       }
> >
> > -    /* Decide whether many devices are supported or not */
> > -    ret = i == ARRAY_SIZE(ioeventfds);
> > +    /* If i equals to 7, many devices are supported */
> > +    ret = i;
> >
> >       while (i-->  0) {
> >           kvm_set_ioeventfd_pio_word(ioeventfds[i], 0, i, false);
> > @@ -1078,8 +1077,6 @@ int kvm_init(void)
> >       kvm_state = s;
> >       memory_listener_register(&kvm_memory_listener, NULL);
> >
> > -    s->many_ioeventfds = kvm_check_many_ioeventfds();
> > -
> >       cpu_interrupt_handler = kvm_handle_interrupt;
> >
> >       return 0;
> > @@ -1407,7 +1404,7 @@ int kvm_has_many_ioeventfds(void)
> >       if (!kvm_enabled()) {
> >           return 0;
> >       }
> > -    return kvm_state->many_ioeventfds;
> > +    return kvm_check_many_ioeventfds();
>
> And why are you dropping the caching of the kvm_check_many_ioeventfds()
> return value? Is kvm_has_many_ioeventfds not used outside init scopes?

Hi Jan,

In the past, kvm_state->many_ioeventfds is only updated once at the 
beginning,
I want to use kvm_check_many_ioeventfds() to check if available 
ioeventfd exists
before starting ioeventfd each time.

--
                        Amos.