Re: [Xen-devel] PV drivers on HVM using Xen 4.1.1

[Alex Bligh <alex@xxxxxxxxxxx>]

--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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