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SubjectRe: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk
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@redhat.com> 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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