On Thu, Mar 29, 2018 at 11:33:29AM +0800, Tiwei Bie wrote: > 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?
I think correctness and security go first before performance. vIOMMU goes under security. > > > > Ability to run dpdk within guest seems important. > > I think vIOMMU isn't a must to run DPDK in guest. Oh yes it is. > For Linux > guest we also have igb_uio and uio_pci_generic to run DPDK, > for FreeBSD guest we have nic_uio. These hacks offer no protection from a buggy userspace corrupting guest kernel memory. Given DPDK is routinely linked into closed source applications, this is not a configuration anyone can support. > They don't need vIOMMU, > and they could offer the best performance. > > Best regards, > Tiwei Bie > > > > > -- > > MST > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org > > For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org > >