Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk

[Asias He]

On 06/18/2012 06:13 PM, Michael S. Tsirkin wrote:
> On Mon, Jun 18, 2012 at 04:03:23PM +0800, Asias He wrote:
> > On 06/18/2012 03:46 PM, Rusty Russell wrote:
> > > On Mon, 18 Jun 2012 14:53:10 +0800, Asias He <asias@xxxxxxxxxx> wrote:
> > > > This patch introduces bio-based IO path for virtio-blk.
> > >
> > > Why make it optional?
> >
> > request-based IO path is useful for users who do not want to bypass
> > the IO scheduler in guest kernel, e.g. users using spinning disk.
> > For users using fast disk device, e.g. SSD device, they can use
> > bio-based IO path.
>
> OK I guess but then it should be per-device. There could be
> a mix of slow and fast disks :)

Yes, per-device might be useful. There are issues which need solving.
- How do we tell the drive which IO path to use
  - Device add some flag
    - Old qemu/lkvm can not turn this feature on
  - Through /sys filesystem attribute
    - How do we handle the switch from one path to anther.

So, let's add the per-device feature later.

--
Asias


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