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Re: [Xen-devel] x86_64 SLES 9 SP2 build break

To: "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
Subject: Re: [Xen-devel] x86_64 SLES 9 SP2 build break
From: Ryan Harper <ryanh@xxxxxxxxxx>
Date: Fri, 19 Aug 2005 13:26:58 -0500
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, David F Barrera <dfbp@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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* Nakajima, Jun <jun.nakajima@xxxxxxxxx> [2005-08-19 13:12]:
> Ryan Harper wrote:
> > * Nakajima, Jun <jun.nakajima@xxxxxxxxx> [2005-08-19 12:14]:
> >> Ian Pratt wrote:
> >>>> Fixing this particular one looks easy, but I realized that
> >>>> cpu hotplug suff is missing in x86_64 xenlinux. I'm making a
> >>>> patch for that.
> >>> 
> >>> Please co-ordinate with Ryan Harper -- he's already working on this.
> >>> 
> >>> Thanks,
> >>> Ian
> >> 
> >> Ryan, Hi
> >> 
> >> If you are already working on it, I just add the missing
> >> hypercall(s) to fix the build problems (and test reboot things).
> >> 
> >> If there is anything that we can help, please let me know. We need
> >> the code ASAP.
> > 
> > You need x86_64 to run ASAP, not HOTPLUG_CPU for x86_64 smp, correct?
> No, we _do_ need HOTPLUG_CPU for x86_64 smp. The build problem is not a
> big deal.

Ah. OK.  I don't think it will be a problem for Xen, but currently in
plain linux-2.6.13-rc6 (which has x86_64 HOTPLUG_CPU support),
support is non-functional, at least on my two-way Opteron box.  I can
remove a cpu (echo 0 > /sys/devices/system/cpu/cpu1/online) fine, but
when I try to restore (echo 1), the processor fails to come back.  Part
of this is that they are integrating the physical hotplug support which
requires a full reboot of the processor (a second run through
do_boot_cpu()) since it would have been physically removed.   I really
wanted to see HOTPLUG_CPU work on plain Linux before bringing the code
into XenLinux, but the issues may be tied up in code that Xen doesn't
need.  The hypervisor will have to support physical hotplug before
XenLinux will need it.  

There are some other subtle differences in HOTPLUG_CPU in the newer
2.6.13 series for x86_64 compared to the level of HOTPLUG_CPU we have
patched into the 2.6.12 tree.

I'll go ahead and work up a patch that brings in HOTPLUG_CPU for x86_64
and share that so we both can work on getting it working.

Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253

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