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

[Mario <mario@xxxxxxxxxxxxxx>]

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.
> http://mirror.orionvm.com.au
>
> 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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