i686 requirements

i686 requirements

[Antonio Vargas]

Regarding XEN requirements to run, I'd like to know if there is any
important reason to require i686-class cpus (ie: ppro, p2, etc.. and
k7...). In my limited understanding of 386 arch, ppro added
conditional moves and PAE, perhaps even huge-pages (have to check this
one). Is XEN explicitely (as in, used directly on assembler code)
using any of these?

My motivation is getting XEN to run on my (aging) k6 server machine.

Greets anyways :)

-- 
Greetz, Antonio Vargas aka winden of network

http://wind.codepixel.com/

Las cosas no son lo que parecen, excepto cuando parecen lo que si son.


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Re: i686 requirements

[Mark Williamson]

Off the top of my head, 3 reasons that I know of:

1) Xen requires a local APIC for its timer functionality.  There is some 
compatibility stuff for non local-APIC chips to enable running VMWare but it 
isn't often used AFAIK.
2) I'm not sure Xen includes all of the skanky fixups for the implementation 
bugs in various older chips anymore.
3) Xen needs an rdtsc instruction and not all older chips have it (although I 
believe there was an implementation in Intel's Pentium not all manufacturers 
included it immediately)

I don't know how much work would be involved in running modern versions of Xen 
on these older machines.  I was going to try this a while back but never got 
round to it and things have moved on since then...

HTH,
Mark

On Friday 07 January 2005 12:34, Antonio Vargas wrote:
> Regarding XEN requirements to run, I'd like to know if there is any
> important reason to require i686-class cpus (ie: ppro, p2, etc.. and
> k7...). In my limited understanding of 386 arch, ppro added
> conditional moves and PAE, perhaps even huge-pages (have to check this
> one). Is XEN explicitely (as in, used directly on assembler code)
> using any of these?
>
> My motivation is getting XEN to run on my (aging) k6 server machine.
>
> Greets anyways :)


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Re: i686 requirements

[Ian Pratt]

> Regarding XEN requirements to run, I'd like to know if there is any
> important reason to require i686-class cpus (ie: ppro, p2, etc.. and
> k7...). In my limited understanding of 386 arch, ppro added
> conditional moves and PAE, perhaps even huge-pages (have to check this
> one). Is XEN explicitely (as in, used directly on assembler code)
> using any of these?

The current Xen code needs 4MB pages (PSE) support. 

There was a patch posted a while back to avoid this constraint,
but I don't think it was fully working. We'd be very happy to
incorporate a patch that adds support for CPUs without PSE,
providing it didn't impact the normal code too much (i.e. didn't
make it less readable). 
 
> My motivation is getting XEN to run on my (aging) k6 server machine.

Chopping a tiny pie into quarters doesn't make it a bigger pie
:-)

Ian


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Re: i686 requirements

[Adam Sulmicki]

> Regarding XEN requirements to run, I'd like to know if there is any
> important reason to require i686-class cpus (ie: ppro, p2, etc.. and
> k7...). In my limited understanding of 386 arch, ppro added
> conditional moves and PAE, perhaps even huge-pages (have to check this
> one). Is XEN explicitely (as in, used directly on assembler code)
> using any of these?

XEN is smart enough not to attempt to use PAE if it not supported.

As far as CMOVE and PSE goes, This my patch posted a while ago will fix 
it. You can find it on web in varous xen archives, for example

 	http://article.gmane.org/gmane.comp.emulators.xen.devel/4062
 	http://sourceforge.net/mailarchive/message.php?msg_id=10258941

it is important to note that it is against xen 2.0.1 so you must use

         bk clone -rRELEASE-2.0.1 bk://xen.bkbits.net/xen-2.0.bk xen-2.0.1.bk

instead of as

         bk clone bk://xen.bkbits.net/xen-2.0.bk

as mentioned in the above said email.

It has worked for me and Rupert Schlick, but other than that it had fairly 
limited testing. So the more ppl test it out the better.

I hope to port it to xen 2.0.2 and xen 2.0-testing eventually.

> My motivation is getting XEN to run on my (aging) k6 server machine.

I'm not that familar with specs of K6 so there migt be other gotchas, but 
I suppose it is worth of a try.


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