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xen-devel
Re: [Xen-devel] PV drivers on HVM using Xen 4.1.1
--On 27 October 2011 15:19:16 +0100 Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
There seems to be some doubt (see Ian's message) about whether this
changes the backend driver that is used. The final deployment application
is tap:aio with a block device, so that's why we're doing this.
If you are using XL, no matter if you specify tap:aio or file:, you are
going to get qemu as disk backend if you are missing blktap.
There is nothing wrong with that, except that qemu in 4.1 doesn't
support linux aio so the performances are not very good. I am not sure
which one is better: blkback on a loop device or qemu without linux aio,
they are both rather slow.
I'm not sure I understand that. blkback on a loop device implies we
can just use blkback on a real device. We are using a real device
anyway in production (the file is just for testing).
So, should we be using tap:aio:/dev/... for a block device for
speed?
In order to make it fast you can:
- use a dom0 kernel that provides blktap;
- use LVM with blkback;
- use upstream qemu with linux aio as device model and/or block backend.
I /think/ you mean only if we are using a file, so that shouldn't
be relevant. Correct?
--
Alex Bligh
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