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Date: Wed, 04 Aug 2010 11:46:34 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with
	Linux 2.6.35?
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To: Avi Kivity <avi@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org, "Richard W.M. Jones" <rjones@redhat.com>, Gleb Natapov <gleb@redhat.com>, qemu-devel@nongnu.org

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 inevitable..
>
> 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 overhead.

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.  It also 
supports SCSI level pass through which is pretty nice for enabling 
things like NPIV.

Regards,

Anthony Liguori