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xen-devel
[Xen-devel] Re: [RFC PATCH 35/35] Add Xen virtual block device driver.
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To: |
Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [RFC PATCH 35/35] Add Xen virtual block device driver. |
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From: |
Rusty Russell <rusty@xxxxxxxxxxxxxxx> |
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Date: |
Sat, 25 Mar 2006 21:03:11 +1100 |
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Cc: |
xen-devel@xxxxxxxxxxxxxxxxxxx, Jeff Garzik <jeff@xxxxxxxxxx>, SCSI Mailing List <linux-scsi@xxxxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Ian Pratt <ian.pratt@xxxxxxxxxxxxx> |
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Sat, 25 Mar 2006 10:04:38 +0000 |
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On Fri, 2006-03-24 at 15:55 +0000, Alan Cox wrote:
> On Gwe, 2006-03-24 at 07:38 -0500, Jeff Garzik wrote:
> > > A pure SCSI abstraction doesn't allow for shared head scheduling which
> > > you will need to scale Xen sanely on typical PC boxes.
> >
> > Not true at all. If you can do it with a block device, you can do it
> > with a SCSI block device.
>
> I don't believe this is true. The complexity of expressing sequences of
> command ordering between virtual machines acting in a co-operative but
> secure manner isn't as far as I can see expressable sanely in SCSI TCQ
I thought usb_scsi taught us that SCSI was overkill for a block
abstraction? I have a much simpler Xen block-device implementation
which seems to perform OK, and is a lot less LOC than the in-tree one,
so I don't think the "SCSI would be better than what's there" (while
possibly true) is valid.
Cheers!
Rusty.
--
ccontrol: http://ozlabs.org/~rusty/ccontrol
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