Mailing List Archive

General questions on IA64 porting
I have now a new IA64 platform (a Bull NovaScale 4020, otherwise sayed an
Intel SR870BH2 platform) and I am ready to participate to the IA64 porting.

I have a few questions about the IA64 porting :

1) The IA64 porting in Xen seems to be stopped or sleeping.
Q: What is the status of Xen-IA64 development ?

2) In the Xen Users' manual, it is sayed "a port to the IA64 architecture
is approching completion". It's seems to be optimistic.
Q: When IA64 support will be officially available ?

3) Several limitations exist on Xen-IA32 (memory <= 4GB, no TLS support,
problem with AGP graphic cards, etc...).
Q: Is these limitations also apply on Xen-IA64 ?

4) Xen-IA32 supports SMP guest OSes.
Q: Is it true also on IA64 ?

5) The Xen architecture is planned to be integrated in Linux sources.
Q: Is this integration also applies to Xen-IA64 and at the same time
than Xen-IA32 or later ?

6) The Linux distributions for IA64 (ie: RHEL-3) are based on Linux 2.4
kernel.
Q: So why IA64 porting is based on Linux 2.6 kernel ? What is the reason ?

7) The RHEL (Red Hat Entreprise Linux) license doesn't permits to modify
or rebuilt the Linux kernel without losing the Red Hat support.
Q: So in case of problems on a customer site, who is responsible ?
Is Xen will provide a direct or indirect support in this case ?

8) How can I help you in the IA64 porting and/or testing ?

Thanks,
Philippe.
Re: General questions on IA64 porting [ In reply to ]
> 1) The IA64 porting in Xen seems to be stopped or sleeping.
> Q: What is the status of Xen-IA64 development ?

It's still alive. Xen/IA64 is Dan Magenheimer's baby and he's been mostly
working on it alone so far. I believe some people from Intel were looking to
contribute too. I've been able to contribute a little time but I have other
things demanding my attention also.

Xen/IA64 currently boots into a single dom0. No serious optimisation has been
done yet.

> 2) In the Xen Users' manual, it is sayed "a port to the IA64 architecture
> is approching completion". It's seems to be optimistic.
> Q: When IA64 support will be officially available ?

That'll probably depend on how many people end up working on it. It'll be
months, at least, I'd speculate.

> 3) Several limitations exist on Xen-IA32 (memory <= 4GB, no TLS support,
> problem with AGP graphic cards, etc...).
> Q: Is these limitations also apply on Xen-IA64 ?

I think Dan had his AGP graphics card working OK.

The memory limitation on Xen/IA32 is purely because nobody has wanted to add
PAE support (we think that IA32 machines with >4gig are relatively rare and
that supporting x86_64 is a more rewarding route to large memory systems).
On IA64 this issue doesn't apply.

The TLS support problem on IA32 is an artifact of the strange way TLS is
implemented on that architecture. Again, I don't expect that it's an issue
on IA64.

> 4) Xen-IA32 supports SMP guest OSes.
> Q: Is it true also on IA64 ?

Not yet. I'm not sure if it'll be worth the effort to support this to start
with, although it will be a goal to support this eventually.

> 5) The Xen architecture is planned to be integrated in Linux sources.
> Q: Is this integration also applies to Xen-IA64 and at the same time
> than Xen-IA32 or later ?

Definitely later. The IA32 code is ready to be merged pretty soon and Andrew
Morton has been making very encouraging noises about it. The IA64 code won't
be ready by then.

The IA64 modifications should be much smaller, so they may be possible to
integrate into the arch/ia64 tree itself.

> 6) The Linux distributions for IA64 (ie: RHEL-3) are based on Linux 2.4
> kernel.
> Q: So why IA64 porting is based on Linux 2.6 kernel ? What is the reason ?

I can't speak for Dan on this but I imagine because it's the kernel of the
future - RHEL 4 will be based on the 2.6 kernel. If Xen/IA64 gets integrated
into a future RHEL, it'll be based on 2.6 anyhow.

> 7) The RHEL (Red Hat Entreprise Linux) license doesn't permits to modify
> or rebuilt the Linux kernel without losing the Red Hat support.
> Q: So in case of problems on a customer site, who is responsible ?
> Is Xen will provide a direct or indirect support in this case ?

Well... I guess future releases of RHEL may integrate Xen support (things
seems to be headed that way for IA32), in which case you won't need to
replace your kernel to get it. Xen/IA64 isn't ready for production use yet,
anyhow.

There'd be some support available on this mailing list and XenSource might be
able to provide some additional support guarantees (regarding the Xen side of
things, anyhow). I'm doubtful that having paid for a RHEL license you'd want
to invalidate the Red Hat support contract, however.

> 8) How can I help you in the IA64 porting and/or testing ?

Dan can probably provide more useful direction here. The first step would be
to get IA64 booting on your machine (the mailing list archives contain
various useful discussions and links regarding this).

Thanks,
Mark


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Re: General questions on IA64 porting [ In reply to ]
Thanks, Mark, for the replies. I'll add only a couple
of comments:

> Q: When IA64 support will be officially available ?

Depends on what you mean by "support". If you mean that
it works approximately as well as Xen/ia32 (perhaps with
some missing functionality such as no SMP guests), that
will hopefully happen in the next few months. If you
mean support as in buying a support contract such as
Xensource might provide, I'd imagine that will be quite
a while longer.

> Q: So why IA64 porting is based on Linux 2.6 kernel ? What is the reason ?

Xen/x86 utilized portions of Linux from approx 2.4.9.
At that point Linux/ia64 support was largely experimental;
many many problems have been fixed since then. So I
had to use another version and decided to start with
2.6.x rather than 2.4.x. As Mark points out, 2.6 support
will be available very soon in RHEL4 and is already
available (I think) in Suse.

Dan




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Re: General questions on IA64 porting [ In reply to ]
> 8) How can I help
> you in the IA64 porting and/or testing ?

Sorry, I forgot to reply to this question. One thing
that would be useful would be some work on the serial
I/O code. Right now, I bypass the UART code in
drivers/char/{serial,console}.c because it does
inb/outb calls to addresses that are incorrect on
ia64. Instead I have a horrible hack that puts out
characters through a routine that is known to work
only on the HP rx2600 and ski simulator. And even for
these it only does output so there's no way to control
Xen/ia64. Since I don't have access to any machines
other than these, it would be hard for me to test any
improvements.

If you have another type of ia64 machine and especially
if you have a good hardware debugger (as its very hard
to debug code when you have no output at all :-), getting
this code to be more portable would be a big contribution.

If possible it would be nice to leverage the existing
Xen/x86 code. There were also a number of recent
"early printk" changes in Linux/ia64 2.6.10 that might
be useful, however it would not be good to pull in all
the Linux tty struct code just to support basic serial
I/O.

Interested?

Thanks,
Dan Magenheimer




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