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Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2

From: Anthony Liguori
Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35?
Date: Wed, 04 Aug 2010 11:49:43 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100713 Lightning/1.0b1 Thunderbird/3.0.6

On 08/04/2010 11:48 AM, Alexander Graf wrote:
On 04.08.2010, at 18:46, Anthony Liguori wrote:

On 08/04/2010 11:44 AM, Avi Kivity wrote:
On 08/04/2010 03:53 PM, Anthony Liguori wrote:
So how do we enable support for more than 20 disks?  I think a virtio-scsi is 
Not only for large numbers of disks, also for JBOD performance.  If you have 
one queue per disk you'll have low queue depths and high interrupt rates.  
Aggregating many spindles into a single queue is important for reducing 
Right, the only question is, to you inject your own bus or do you just reuse 
SCSI.  On the surface, it seems like reusing SCSI has a significant number of 
advantages.  For instance, without changing the guest's drivers, we can 
implement PV cdroms or PC tape drivers.
What exactly would keep us from doing that with virtio-blk? I thought that 
supports scsi commands already.

I think the toughest change would be making it appear as a scsi device within the guest. You could do that to virtio-blk but it would be a flag day as reasonable configured guests will break.

Having virtio-blk device show up as /dev/vdX was a big mistake. It's been nothing but a giant PITA. There is an amazing amount of software that only looks at /dev/sd* and /dev/hd*.


Anthony Liguori


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