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Re: [Qemu-devel] [PATCH 1/6] virtio: introduce virtio_map
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [Qemu-devel] [PATCH 1/6] virtio: introduce virtio_map |
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Date: |
Tue, 27 Oct 2015 20:34:32 +0200 |
On Tue, Oct 27, 2015 at 04:19:54PM +0000, Stefan Hajnoczi wrote:
> On Tue, Oct 27, 2015 at 10:47:56AM +0200, Michael S. Tsirkin wrote:
> > This will still fail if there's no space left in the sg, but luckily max
> > queue size in use is currently 256, while max sg size is 1024, so we
> > should be OK even is all entries happen to cross a single DIMM boundary.
>
> Don't forget about indirect descriptors. They can use all 1024 iovecs,
> regardless of virtqueue size, so virtqueue size of 256 isn't the true
> maximum.
Not according to the spec - virtio spec says vq size is the maximum size
of a chain.
> I'm worried that we could now see failures due to non-contiguous HVAs.
Does linux guest create chains > vq size then? Does it actually
have 1024 hardcoded somewhere?
--
MST
- [Qemu-devel] [PATCH 0/6] virtio: handle non contigious s/g entries, Michael S. Tsirkin, 2015/10/27
- [Qemu-devel] [PATCH 2/6] virtio: switch to virtio_map, Michael S. Tsirkin, 2015/10/27
- [Qemu-devel] [PATCH 4/6] virtio-serial: convert to virtio_map, Michael S. Tsirkin, 2015/10/27
- [Qemu-devel] [PATCH 3/6] virtio-blk: convert to virtqueue_map, Michael S. Tsirkin, 2015/10/27
- [Qemu-devel] [PATCH 5/6] virtio-scsi: convert to virtqueue_map, Michael S. Tsirkin, 2015/10/27