[PATCH for 4.7] doc: document that Domain-0 can't be migrated across cpupools

[PATCH for 4.7] doc: document that Domain-0 can't be migrated across cpupools

[Juergen Gross]

Domain-0 is always member of Pool-0 (or, to be precise: of the cpuppol
with cpupool-id 0). Document this in the xl man page.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 docs/man/xl.pod.1 | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1
index e2bd32d..9887f1b 100644
--- a/docs/man/xl.pod.1
+++ b/docs/man/xl.pod.1
@@ -1263,6 +1263,7 @@ exact same syntax as in B<cpupool-cpu-add> above.
 =item B<cpupool-migrate> I<domain> I<cpu-pool>
 
 Moves a domain specified by domain-id or domain-name into a cpu-pool.
+Domain-0 can't be moved to another cpu-pool.
 
 =item B<cpupool-numa-split>
 
-- 
2.6.6


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Re: [PATCH for 4.7] doc: document that Domain-0 can't be migrated across cpupools

[Andrew Cooper]

On 09/05/2016 09:29, Juergen Gross wrote:
> Domain-0 is always member of Pool-0 (or, to be precise: of the cpuppol
> with cpupool-id 0). Document this in the xl man page.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>

Out of interest, why?

Is this a limitation of the current implementation, or something which
couldn't be made to work?

Given that it is all just vcpus and linked lists in the end, I can't see
why this should necessarily be the case.

~Andrew

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Re: [PATCH for 4.7] doc: document that Domain-0 can't be migrated across cpupools

[Juergen Gross]

On 09/05/16 10:36, Andrew Cooper wrote:
> On 09/05/2016 09:29, Juergen Gross wrote:
>> Domain-0 is always member of Pool-0 (or, to be precise: of the cpuppol
>> with cpupool-id 0). Document this in the xl man page.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
> 
> Out of interest, why?
> 
> Is this a limitation of the current implementation, or something which
> couldn't be made to work?
> 
> Given that it is all just vcpus and linked lists in the end, I can't see
> why this should necessarily be the case.

Main reason was to keep cpu hotplugging simple. New cpus are always
added to Pool-0 and should be available to dom0 immediately without
having to move them to another cpupool.

It could be changed, of course. But I don't see any advantage in
allowing to move dom0 to another cpupool, while the code would be
more complicated.


Juergen


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Re: [PATCH for 4.7] doc: document that Domain-0 can't be migrated across cpupools

[Wei Liu]

On Mon, May 09, 2016 at 10:53:30AM +0200, Juergen Gross wrote:
> On 09/05/16 10:36, Andrew Cooper wrote:
> > On 09/05/2016 09:29, Juergen Gross wrote:
> >> Domain-0 is always member of Pool-0 (or, to be precise: of the cpuppol
> >> with cpupool-id 0). Document this in the xl man page.
> >>
> >> Signed-off-by: Juergen Gross <jgross@suse.com>
> > 
> > Out of interest, why?
> > 
> > Is this a limitation of the current implementation, or something which
> > couldn't be made to work?
> > 
> > Given that it is all just vcpus and linked lists in the end, I can't see
> > why this should necessarily be the case.
> 
> Main reason was to keep cpu hotplugging simple. New cpus are always
> added to Pool-0 and should be available to dom0 immediately without
> having to move them to another cpupool.
> 
> It could be changed, of course. But I don't see any advantage in
> allowing to move dom0 to another cpupool, while the code would be
> more complicated.
> 
> 

I think this patch is valid in that it documents the current situation.
Whether migration of Dom0 should be supported or not is a separate
topic.

Acked-by: Wei Liu <wei.liu2@citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

I've queued this up for committing.

Wei.

> Juergen
> 

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