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

[Amos Kong <akong@redhat.com>]

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<akong@redhat.com>
>> ---
>>   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.