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Re: [Xen-users] HVM on 3.2 kernel hdd speed issue

On 04/02/2012 09:55 PM, Joseph Glanville wrote:
On 3 April 2012 05:48, Mario<mario@xxxxxxxxxxxxxx>  wrote:
On 04/02/2012 09:27 PM, Joseph Glanville wrote:

On 3 April 2012 05:17, Mario<mario@xxxxxxxxxxxxxx>    wrote:

On 04/02/2012 08:45 PM, Joseph Glanville wrote:

On 2 April 2012 22:49, Mario<mario@xxxxxxxxxxxxxx>      wrote:

On 04/02/2012 01:55 PM, Heiko Wundram wrote:

Am 02.04.2012 13:33, schrieb Mario:

On 04/02/2012 12:19 PM, Heiko Wundram wrote:

Windows, of course, does not natively support PVonHVM in any way
when using corresponding drivers to enable that), so if you get
excessively slower I/O-speeds on "fully" virtualized Linux DomUs
you do on Windows DomUs which _don't_ have the corresponding
installed, something else is amiss here; it'd help if you could
your setup in a little more detail.

Why are we still on PVonHVM subject? I do not want that, I want
regular HVM to work with linux domU's the same way it works with
windows domU's. I don't have the luxury to install custom drivers on
some domU's, so there is no point in trying to force me to use
because i can't.
So, anyone else please? :-)

Read my last paragraph again, please: Linux fully virtualized DomUs
(which use the corresponding NIC and disk emulation as implemented by
qemu) shouldn't perform any different than a Windows DomU,
I/O-performance wise, as both of them use the same infrastructure in
Dom0 to do I/O (qemu process). You're saying that they are different,
I/O-wise, so: please be a little more concrete _what_ the problem is
that you're seeing. We don't have crystal balls handy, sorry.

Its actualy quite simple, here is an example: Windows hvm domU disk io
test server is ~60MB/s (sequential read or write). Linux HVM guests
same config file template) on the same server gives ~10MB/s (sequential
or write), i tried pretty much everything, from tuning scheduler to
kernel. I am not sure what to do with it, other then roll back to
2.6.34 on my dom0.

Hieko and myself have told you what to do to get decent performance.
Some examples of fully setup PVonHVM guests are available on my file

Unless you use the PV drivers there isn't really a whole lot more I
can do for you.

I can't explain why performance would differ under 2.6.34 vs 3.2.
This makes no sense as qemu-dm runs in userspace. You would have had to
some changes to the toolstack for this performance to differ.

Performance difference between dom0 kernels aside, what I don't
is why windows HVM domU works fine, while linux doesn't?
Isn't HVM supposed to work same for every guest, or does linux actualy
something against HVM mode? I simply don't get it.

It's definitely not an optimized use case however I have never seen as
low performance as you are reporting.
There are too many reasons to list as to why performance between
Windows HVM and Linux HVM would differ.

What Linux guests are you attempting to run?


Running a slackware guest, tried various kernels, did not make any
difference. Windows in question is 2008 R2.

Try using a 3.0 guest kernel with XEN_PLATFORM_PCI=y and all of the
Xen device drivers.
This will enable PVHVM and you should be right as rain for performance.

So what exactly do I do with linux guests that I don't have kernel sources for? :-)

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