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Subject: Re: [virtio-dev] Re: [PATCH v2 0/6] Extend vhost-user to support VFIO based accelerators
On Wed, Mar 28, 2018 at 06:33:01PM +0300, Michael S. Tsirkin wrote: > On Wed, Mar 28, 2018 at 08:24:07PM +0800, Tiwei Bie wrote: > > > > Update notes > > > > ============ > > > > > > > > IOMMU feature bit check is removed in this version, because: > > > > > > > > The IOMMU feature is negotiable, when an accelerator is used and > > > > it doesn't support virtual IOMMU, its driver just won't provide > > > > this feature bit when vhost library querying its features. And if > > > > it supports the virtual IOMMU, its driver can provide this feature > > > > bit. It's not reasonable to add this limitation in this patch set. > > > > > > Fair enough. Still: > > > Can hardware on intel platforms actually support IOTLB requests? > > > Don't you need to add support for vIOMMU shadowing instead? > > > > > > > For the hardware I have, I guess they can't for now. > > So VFIO in QEMU has support for vIOMMU shadowing. > Can you use that somehow? Yeah, I guess we can use it in some way. Actually supporting vIOMMU is a quite interesting feature. It would provide better security, and for the hardware backend case there would be no performance penalty with static mapping after the backend got all the mappings. I think it could be done as another work. Based on your previous suggestion in this thread, I have split the guest notification offload and host notification offload (I'll send the new version very soon). And I plan to let this patch set just focus on fixing the most critical performance issue - the host notification offload. With this fix, using hardware backend in vhost-user could get a very big performance boost and become much more practicable. So maybe we can focus on fixing this critical performance issue first. How do you think? > > Ability to run dpdk within guest seems important. I think vIOMMU isn't a must to run DPDK in guest. For Linux guest we also have igb_uio and uio_pci_generic to run DPDK, for FreeBSD guest we have nic_uio. They don't need vIOMMU, and they could offer the best performance. Best regards, Tiwei Bie > > -- > MST > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org >
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