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

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Message-ID: <4FDFE22E.3030003@redhat.com>
Date:	Tue, 19 Jun 2012 10:21:34 +0800
From:	Asias He <asias@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Christoph Hellwig <hch@....de>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [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@...hat.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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