RE: [Xen-users] Release 0.9.5 of GPL PV Drivers for Windows

["Geoff Wiener" <gwiener@xxxxxxxxxxxxxxx>]

Hi James;

Hopefully I am now the bearer of good news.  After our last volley I
understood that you have not been testing your drivers with blktap (as
it is not compiled in your Debian kernel).

So I decided to run the tests again using:

disk = [ 'file:/xenimages/w2k3/pv.img,hda,w']

The difference was astounding!  Have a look at the attached .jpg.  The
column in purple is configured as above.  The performance kills
everything else so far.  Then I started thinking about the disk line
itself  From what I understand, the reason we specify "hda" for HVM
guests is that until your drivers came along (in the GPL world) HVM
guests did not have support for xvd devices.  I'm going to quote from a
book so hopefully this complete reference covers me off:  (Great book
BTW:)

Matthews Jeanna, N. 2008. Using Prebuilt Guest Images: Introduction to
DomU guests, Running Xen, A Hands-On Guide to the Art of Virtualization.
Prentice Hall

"The xvd devices interface allows the Xen guest to understand that it
has virtual disks instead of native hardware.  The xvd interface
exploits this knowledge to achieve better performance.<snip>:  With HVM
guests that do not have paravirtual block device drivers installed, you
still need to use the hd (IDE) and sd (SCS) disks for the DOmU, because,
" by default, HVM guests do not ahve support for xvd devices.

So with that bit of information I went ahead and modified my disk line
as follows:

disk = [ 'file:/xenimages/w2k3/pv.img,xvda,w']

and then ran the tests again.  A side note, when the DomU booted it
PnP'ed your Xen Block Device Driver again, I thought that in itself was
interesting.  The column in red details the performance after changing
the disk line.  You will see that in some cases the performance was
about the same but in others there was a massive improvement.  Have a
look, in particular, at the new section I added called "Heavy Write".  I
captured this particular workload from a naughty database application
that we host for one of our customers.  The best performance that I have
been able to achieve for that particular app, using a very high spec SAN
is detailed in the column to the right labelled "SAN".

The next logical test was to try to use the blktap driver again.  No joy
- BSDO city.  Just so I am clear in my understanding and please remember
I am a complete NooB with regards to Xen, I am under the impression that
the "file:" prefix is "depreciated" and the blktap driver is the
preferred method of connecting to disk files?  Is there some official
documentation on this somewhere?  And if this is the case, from what I
understand blktap should perform even better than the loopback driver
that file: is using.  (at least that has been my experience in other
environments).  So if everything I think I understand is true, what can
we do about getting you a Xen 3.2.1 installation with blktap enabled for
you to develop on?  I am open to suggestions about how to get you
sorted.  For starters, I have recently been through the pain and
suffering of installing on Centos 5.1, I would be happy to share my
installation notes with you.

Congratulations James, configured correctly your drivers are a huge
success!

Best Regards

Geoff


-----Original Message-----
From: James Harper [mailto:james.harper@xxxxxxxxxxxxxxxx] 
Sent: 02 June 2008 12:59 PM
To: Geoff Wiener; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] Release 0.9.5 of GPL PV Drivers for Windows

> Hi James;
> 
> >All your examples above say 'domain0' instead of 'domain/0'. Could
that
> be the problem or did you just make a typo in copying it into the
email?
> 
> You are right, my bad - I was typing the command wrong - it should be
> domain/0.  The output you want is:
> 
> domain = "qcow"
> frontend = "/local/domain/75/device/vbd/768"
> uuid = "b01d6f19-e818-f976-a284-ed9a3097d857"
> dev = "hda"
> state = "2"
> params = "qcow:/xenimages/w2k3/w2k3.qcow"
> mode = "w"
> online = "1"
> frontend-id = "75"
> type = "tap"
> hotplug-status = "connected"
> 
> I will have a look at debugview next.
> 

Thanks. I had a go myself but I'm using Debian, and
CONFIG_XEN_BLKDEV_TAP is not enabled in the Debian kernels so I'm stuck
without blktap...

James

Attachment: Xen PVGPL xvda.JPG
Description: Xen PVGPL xvda.JPG

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