Re: [Qemu-devel] [PATCH] virtio-serial: Allow one MSI-X vector per virtqueue

[Zang Hongyong <zanghongyong@huawei.com>]

于 2011/12/16,星期五 17:39, Amit Shah 写道:
> On (Fri) 16 Dec 2011 [09:14:26], zanghongyong@huawei.com wrote:
>> From: Hongyong Zang<zanghongyong@huawei.com>
>>
>> In pci_enable_msix(), the guest's virtio-serial driver tries to set msi-x
>> with one vector per queue. But it fails and eventually all virtio-serial
>> ports share one MSI-X vector. Because every virtio-serial port has *two*
>> virtqueues, virtio-serial needs (port+1)*2 vectors other than (port+1).
> Ouch, good catch.
>
> One comment below:
>
>> This patch allows every virtqueue to have its own MSI-X vector.
>> (When the MSI-X vectors needed are more than MSIX_MAX_ENTRIES defined in
>> qemu: msix.c, all the queues still share one MSI-X vector as before.)
>>
>> Signed-off-by: Hongyong Zang<zanghongyong@huawei.com>
>> ---
>>   hw/virtio-pci.c |    5 ++++-
>>   1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
>> index 77b75bc..2c9c6fb 100644
>> --- a/hw/virtio-pci.c
>> +++ b/hw/virtio-pci.c
>> @@ -718,8 +718,11 @@ static int virtio_serial_init_pci(PCIDevice *pci_dev)
>>           return -1;
>>       }
>>       vdev->nvectors = proxy->nvectors == DEV_NVECTORS_UNSPECIFIED
>> -                                        ? proxy->serial.max_virtserial_ports + 1
>> +                                        ? (proxy->serial.max_virtserial_ports + 1) * 2
>>                                           : proxy->nvectors;
>> +    /*msix.c: #define MSIX_MAX_ENTRIES 32*/
>> +    if (vdev->nvectors>  32)
>> +        vdev->nvectors = 32;
> This change isn't needed: if the proxy->nvectors value exceeds the max
> allowed, virtio_init_pci() will end up using a shared vector instead
> of separate ones.
>
> Thanks,
>
> 		Amit
>
> .
>
Hi Amit,
If the nvectors exceeds the max, msix_init() will return -EINVAL in QEMU,
and the front-end driver in Guest will use regular interrupt instead of 
MSI-X.

Hongyong