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

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 (except
when using corresponding drivers to enable that), so if you get
excessively slower I/O-speeds on "fully" virtualized Linux DomUs than
you do on Windows DomUs which _don't_ have the corresponding PV-drivers
installed, something else is amiss here; it'd help if you could describe
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 PVonHVM
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 on my
test server is ~60MB/s (sequential read or write). Linux HVM guests (using
same config file template) on the same server gives ~10MB/s (sequential read
or write), i tried pretty much everything, from tuning scheduler to changing
kernel. I am not sure what to do with it, other then roll back to kernel
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 mirror.

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 make
some changes to the toolstack for this performance to differ.

Performance difference between dom0 kernels aside, what I don't understand 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 have something against HVM mode? I simply don't get it.

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