On 2014/11/6 9:59, Shannon Zhao wrote:

On 2014/11/5 16:43, Eric Auger wrote:

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On 10/27/2014 12:23 PM, Li Liu wrote:

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On 2014/10/27 17:37, Peter Maydell wrote:

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On 25 October 2014 09:24, john.liuli [off-list ref] wrote:

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To get the interrupt reason to support such VIRTIO_NET_F_STATUS
features I add a new register offset VIRTIO_MMIO_ISRMEM which
will help to establish a shared memory region between qemu and
virtio-mmio device. Then the interrupt reason can be accessed by
guest driver through this region. At the same time, the virtio-mmio
dirver check this region to see irqfd is supported or not during
the irq handler registration, and different handler will be assigned.

If you want to add a new register you should probably propose
an update to the virtio spec. However, it seems to me it would
be better to get generic PCI/PCIe working on the ARM virt
board instead; then we can let virtio-mmio quietly fade away.
This has been on the todo list for ages (and there have been
RFC patches posted for plain PCI), it's just nobody's had time
to work on it.

thanks
-- PMM

So you mean virtio-mmio will be replaced by PCI/PCIe on ARM at last?
If so, let this patch go with the wind:). Thx.

Hi,

As a fix of current situation where ISR is only partially updated when
vhost-irqfd handles standard IRQ and waiting for PCI emuluation,
wouldn't it make sense to store ISR content on vhost driver side and
introduce ioctls to read/write it. When using vhost BE, virtio QEMU
device would use those ioctl to read/update the ISR content. On top of
that we would update the ISR in vhost before triggering the irqfd. If I
do not miss anything this would at least make things functional with irqfd.

As a second step, we could try to introduce in-kernel emulation of
ISR/ACK to fix the performance issue related to going to user-side each
time ISR/ACK accesses are done.

Do you think it is worth investigating this direction?

Hi,

About this problem I have a talk with Li Liu. As MST said, we could use
multiple GSI to support vhost-net with irqfd. And we have figured out a way
to solve this problem. The method is as same as virtio-pci which is to assign
multiple irqs for virtio-mmio. Also it can support multiqueue virtio-net on arm.

Would you have a look at this method? Thank you very much.

- virtio-mmio: support for multiple irqs
http://www.spinics.net/lists/kernel/msg1858860.html

Thanks,
Shannon

Yeah, I think multiple GSI is more compatible with MSI-X. And even virtio-mmio
will fade away at last. It still make senses for ARM32 which can't support PCI/PCIe.

BTW, this patch is handed over to Shannon and please refer to new patch at
http://www.spinics.net/lists/kernel/msg1858860.html.

Li.

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Thank you in advance

Best Regards

Eric

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Li.

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