[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] libxl: switch NetBSD image file handling to Qemu
On 28/11/12 14:26, Thor Lancelot Simon wrote: > On Wed, Nov 28, 2012 at 02:20:51PM +0100, Roger Pau Monne wrote: >> This forces libxl to use Qemu when a raw image file is used as a disk >> backend. NetBSD currently only supports qemu-traditional, so > > Wait -- do I grasp correctly that this patch _forces_ NetBSD as a dom0 > to handle file-backed I/O requests in a way that includes additional > context switches to userspace, and which your previous email said > resulted in a 30% reduction in throughput compared to dom0 I/O? > > I am assuming there's some reason we want this, rather than handling > such requests in-kernel. But what is it? I should have marked this as "experimental", or something like this. I'm not sure if switching to Qdisk for all image file backends is needed. >From the Xen wiki (http://wiki.xen.org/wiki/Blktap) I've found that: "loop device had problems with flushing dirty pages (specifically, doing a large number of writes to an NFS-backed image don't result in the OOM killer going berserk)." I'm not sure if NetBSD is in the same situation, but if I remember correctly (haven't tried that in a long time), trying to use a disk file on a NFS share caused the NetBSD Dom0 kernel to crash. The PR for this issue is: http://gnats.netbsd.org/40726. If this is solved, and the vnd device is solid in NetBSD we could only use Qdisk when the image format is different than raw (qcow, qcow2, vmdk, vdi...). _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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