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From: | Paolo Bonzini |
Subject: | Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock |
Date: | Thu, 27 Sep 2012 12:22:41 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 |
Il 27/09/2012 12:08, Avi Kivity ha scritto: >>>>> virtio-net is per-spec not going through the iommu. >>> >> What's that smell? A feature bit? >> > >> > Why is it a bad thing that it does not go through the iommu? > You can't assign the device to nested guests or to guest userspace via > vfio. Some guests may want to use the iommu even in the guest kernel > context. All good points. However, using the iommu means you cannot use either vhost-net or (at least for now) per-device lock. So it closes some doors on performance improvements... I can imagine pSeries guys prefer to keep no iommu in virtio devices. Paolo
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