Xen and VMware

Xen and VMware

[Tim Freeman]

This is an interesting interview with a VMware executive about Xen.  One of
his statements is that Xen is "purely for Linux."

http://blogs.zdnet.com/BTL/index.php?p=1055


Tim


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RE: Xen and VMware

[Tom Hibbert]

Typical corporate talking head blah. Interesting that he talks about
Vmotion as a 'killer technology' when Xen is already doing it. 
If you read the interview there's quite a bit of Xen-bashing. The guy
rags on the requirement for modification of the host kernel. He is
comparing the two products as if they took the same approach, failing to
mention that Xen's paravirtualisation architecture eliminates all of the
costly performance overhead his company's product is famous for...
 

-----Original Message-----
From: xen-devel-admin@lists.sourceforge.net
[mailto:xen-devel-admin@lists.sourceforge.net] On Behalf Of Tim Freeman
Sent: Thursday, 17 February 2005 4:09 a.m.
To: xen-devel@lists.sourceforge.net
Subject: [Xen-devel] Xen and VMware

This is an interesting interview with a VMware executive about Xen.  One
of his statements is that Xen is "purely for Linux."

http://blogs.zdnet.com/BTL/index.php?p=1055


Tim



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Re: Xen and VMware

[Jacob Gorm Hansen]

Tom Hibbert wrote:
> Typical corporate talking head blah. Interesting that he talks about
> Vmotion as a 'killer technology' when Xen is already doing it. 
> If you read the interview there's quite a bit of Xen-bashing. The guy
> rags on the requirement for modification of the host kernel. He is
> comparing the two products as if they took the same approach, failing to
> mention that Xen's paravirtualisation architecture eliminates all of the
> costly performance overhead his company's product is famous for...

I still think you need to respect VMWare for breathing new life into 
virtual machine research. And I still think Xen can be improved (as is 
happening now) with regards to memory footprint etc. VMWare ESX is also 
likely to have some performance benefits from having the drivers in the 
kernel, even though that comes at the cost of them having to implement 
the drivers themselves. And the fact that they can host Windows is a big 
win with lots of customers.

VMWare does some amount of paravirtualization, with all the VMWare tools 
that you need to install. In fact, Xen seems to be going in VMWare's 
direction (shadow page tables, writable page tables, binary rewriting, 
Vanderpool support) in some areas.

The fact that I seem to have prior art for their 'killer technology' I 
just find kind of funny ;-)

Jacob


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Re: Xen and VMware

[aq]

On Wed, 16 Feb 2005 14:50:23 -0800, Jacob Gorm Hansen <jacobg@diku.dk> wrote:
> Tom Hibbert wrote:
> > Typical corporate talking head blah. Interesting that he talks about
> > Vmotion as a 'killer technology' when Xen is already doing it.
> > If you read the interview there's quite a bit of Xen-bashing. The guy
> > rags on the requirement for modification of the host kernel. He is
> > comparing the two products as if they took the same approach, failing to
> > mention that Xen's paravirtualisation architecture eliminates all of the
> > costly performance overhead his company's product is famous for...
> 
> I still think you need to respect VMWare for breathing new life into
> virtual machine research. And I still think Xen can be improved (as is
> happening now) with regards to memory footprint etc. VMWare ESX is also
> likely to have some performance benefits from having the drivers in the
> kernel, even though that comes at the cost of them having to implement
> the drivers themselves. And the fact that they can host Windows is a big
> win with lots of customers.
> 
> VMWare does some amount of paravirtualization, with all the VMWare tools
> that you need to install. In fact, Xen seems to be going in VMWare's
> direction (shadow page tables, writable page tables, binary rewriting,
> Vanderpool support) in some areas.

Jacob, I am surprised here. Which code in Xen that does "binary rewriting"?

Thank you,
AQ


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Re: Xen and VMware

[Jacob Gorm Hansen]

aq wrote:
> On Wed, 16 Feb 2005 14:50:23 -0800, Jacob Gorm Hansen <jacobg@diku.dk> wrote:
> 

>>VMWare does some amount of paravirtualization, with all the VMWare tools
>>that you need to install. In fact, Xen seems to be going in VMWare's
>>direction (shadow page tables, writable page tables, binary rewriting,
>>Vanderpool support) in some areas.
> 
> 
> Jacob, I am surprised here. Which code in Xen that does "binary rewriting"?

I am not sure if it is still there, but one of the approaches to fixing 
the /lib/tls issue was to use binary rewriting of code within the guest OS.

Jacob


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Re: Xen and VMware

[Steven Hand]

> Tom Hibbert wrote:
> > Typical corporate talking head blah. Interesting that he talks about
> > Vmotion as a 'killer technology' when Xen is already doing it. 
> > If you read the interview there's quite a bit of Xen-bashing. The guy
> > rags on the requirement for modification of the host kernel. He is
> > comparing the two products as if they took the same approach, failing to
> > mention that Xen's paravirtualisation architecture eliminates all of the
> > costly performance overhead his company's product is famous for...
> 
> I still think you need to respect VMWare for breathing new life into 
> virtual machine research. And I still think Xen can be improved (as is 
> happening now) with regards to memory footprint etc. VMWare ESX is also 
> likely to have some performance benefits from having the drivers in the 
> kernel, even though that comes at the cost of them having to implement 
> the drivers themselves. And the fact that they can host Windows is a big 
> win with lots of customers.

VMWare deserve respect for doing a /heroic/ engineering job; there are
(as we all know) a bunch of really tricky hurdles to get over in order
to do full (or almost full) virtualization on regular x86 hardware. I 
imagine there is some incredibly intricate and hairy code in there to
deal with the binary scanning + rewriting, etc. 

That said, they may be solving the /wrong/ problem. As Xen (and other
systems, e.g. exokernel) have demonstrated, most punters don't give a 
damn if their OS is bit for bit identical or not providing all of their
applications run correctly. Doing all the heavy lifting of full 
virtualization means that you have lots of complex (and fragile) code, 
and also pay a hefty performance cost. It only makes sense if you 
want to play the licensing game... which is kinda up in the air at 
the moment (e.g. if you experience difficulties w/ windows under vmware
you need to reliably reproduce it under a vanilla install too or MS 
won't support it). 


> VMWare does some amount of paravirtualization, with all the VMWare tools 
> that you need to install. In fact, Xen seems to be going in VMWare's 
> direction (shadow page tables, writable page tables, binary rewriting, 
> Vanderpool support) in some areas.

Hmm: 

  - our shadow page tables are quite different to VMware's (as far as 
    we can tell - there's no docs on their implementation details) 

  - I don't think that writable page tables are something VMWare do 
    since it only makes sense for paravirtualized memory systems.

  - our binary rewriting is a tiny fraction of what they do and, in 
    current default installs of xen 2.x, is not used at all. 

  - we released VT support back in 2004; I don't believe VMWare 
    ship anything supporting VT at present. 

Anyway, the game may well change with the advent of VT and Pacifica; 
there are certainly both technical and legal/economic challenges to 
be overcome. 


cheers,

S.


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Re: Xen and VMware

[Jacob Gorm Hansen]

Steven Hand wrote:

>>VMWare does some amount of paravirtualization, with all the VMWare tools 
>>that you need to install. In fact, Xen seems to be going in VMWare's 
>>direction (shadow page tables, writable page tables, binary rewriting, 
>>Vanderpool support) in some areas.
> 
> Hmm: 
> 
>   - our shadow page tables are quite different to VMware's (as far as 
>     we can tell - there's no docs on their implementation details) 
> 
>   - I don't think that writable page tables are something VMWare do 
>     since it only makes sense for paravirtualized memory systems.
> 
>   - our binary rewriting is a tiny fraction of what they do and, in 
>     current default installs of xen 2.x, is not used at all. 
> 
>   - we released VT support back in 2004; I don't believe VMWare 
>     ship anything supporting VT at present. 

What I meant by that is that where Xen1 was purely in the paravirt camp, 
recent versions take more of a middle-of-the road stance, as Xen now 
sports functionality that does not strictly _have_ to be in the VMM, and 
does so in order to reduce the porting effort for new guest OSes.

Jacob


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Re: Xen and VMware

[Ronald G. Minnich]

On Thu, 17 Feb 2005, Steven Hand wrote:

> That said, they may be solving the /wrong/ problem. 

I'm not so sure that is correct. I've talked to people in the commercial 
world and learned some interesting things. A big use of vmware and citrix 
is to run windows under windows. Why? Because nobody trusts windows or 
windows users. They run citrix (and I guess vmware in other places) 4 or 5 
instances at a time under NT server and use KVMs. This one person I talked 
to ran thousands of desktops this way.

I'm guessing based on some of my conversations that the big end use of 
vmware is windows under windows. But I could be totally wrong. 

ron


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Re: Xen and VMware

[B.G. Bruce]

Actually, the biggest appeal of vmware is being able to run windows in a
vm.  Most organizations don't really care what is underlying, but it's
the ability to snapshot and restore a virtual machine to a known working
condition (particularly with windows) that appeals.  The faster this
restore happens, the better.  They want the ability to immediately back
out a hotfix or service pack (or any other software upgrade or config.
change) that is causing issues and know that "ALL" traces of the
offending change have been removed - immediately.  No fussing around
with regedit or dll version skew.  This is especially true with terminal
servers.  If you have your corporate desktop sitting on a terminal
server (say 250-500) users and someone infects the box with a virus or
spyware, the faster you can get the box back to a pristine working
condition, the more of a hero you look.  It's the same reason large
corporations look to ghost for their desktop builds.  


On Thu, 2005-02-17 at 11:51, Ronald G. Minnich wrote:
> On Thu, 17 Feb 2005, Steven Hand wrote:
> 
> > That said, they may be solving the /wrong/ problem. 
> 
> I'm not so sure that is correct. I've talked to people in the commercial 
> world and learned some interesting things. A big use of vmware and citrix 
> is to run windows under windows. Why? Because nobody trusts windows or 
> windows users. They run citrix (and I guess vmware in other places) 4 or 5 
> instances at a time under NT server and use KVMs. This one person I talked 
> to ran thousands of desktops this way.
> 
> I'm guessing based on some of my conversations that the big end use of 
> vmware is windows under windows. But I could be totally wrong. 
> 
> ron
> 
> 
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