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Re: [libvirt] [PATCH 09/18] Add virtio-related options to interfaces





On 2017年05月30日 21:09, Daniel P. Berrange wrote:
On Tue, May 30, 2017 at 02:50:32PM +0200, Ján Tomko wrote:
<interface type='user'>
   <mac address='52:54:56:5a:5c:5e'/>
   <model type='virtio'/>
   <driver iommu_platform='on' ats='on'/>
</interface>
Feels like we could just use  'iommu=on' as the name.

Also, I'm unclear whether we actually need the 'ats' attribute.

 From the description it sounds like if we have device_iotlb=on
for the IOMMU device, then we should have ats=on too. Is there
a  reason to use ats=off when device_iotlb=on, or vica-verca.
If not, then we should just do the right thing and set ats=on
whenever we see device_iotlb=on.

Maybe for virtio-net only. Vhost can get best performance only when both were set, disabling either will be slower. For the cases of non vhost and other virtio devices, enabling ATS maybe a little bit slower since we don't implement device IOTLB in the device now (though we may want to implement it in the future). So for now, it's better to leave a choice for user.

Another problem is, ATS depends on PCIE, there's some requirement e.g qemu does not support an integrated PCIE device which means we may need a PCIE switch (pcie-root-port) to make PCIE and ATS works.

Thanks

Regards,
Daniel


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