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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: Tue, 03 Aug 2010 16:34:53 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100713 Lightning/1.0b1 Thunderbird/3.0.6

On 08/03/2010 04:13 PM, Paolo Bonzini wrote:
On 08/03/2010 10:49 PM, Anthony Liguori wrote:
On the other hand we end up with stuff like only being able to add 29
virtio-blk devices to a single guest.  As best as I can tell, this
comes from PCI

No, this comes from us being too clever for our own good and not
following the way hardware does it.

All modern systems keep disks on their own dedicated bus.  In
virtio-blk, we have a 1-1 relationship between disks and PCI devices.
That's a perfect example of what happens when we try to "improve" things.

Comparing (from personal experience) the complexity of the Windows drivers for Xen and virtio shows that it's not a bad idea at all.

Not quite sure what you're suggesting, but I could have been clearer. Instead of having virtio-blk where a virtio disk has a 1-1 mapping to a PCI device, we probably should have just done virtio-scsi.

Since most OSes have a SCSI-centric block layer, it would have resulted in much simpler drivers and we could support more than 1 disk per PCI slot. I had thought Christoph was working on such a device at some point in time...


Anthony Liguori


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