RE: [Xen-devel] [PATCH] Fix xmexamples about cpus

[Masaki Kanno <kanno.masaki@xxxxxxxxxxxxxx>]

Hi Ian,

Fri, 9 May 2008 13:07:31 +0100, "Ian Pratt" wrote:

>> >Hi Kanno,
>> >    We have tried cpus="^1" in the past. For we want to drop only CPU1
>> >no matter how many CPUs are on the machine. The result shows: CPU1 can
>> >still be used by HVM and all the VCPU's affinity are "any cpu".
>> >    So, do you think this setting is available? Or do we need some more
>> >comments on this? Thanks!
>> 
>> Hi Zhang,
>> 
>> I think that a purpose to set "cpus" is to confine CPUs which VCPUs run
>> to a CPU or some CPUs.  If there are many CPUs on a machine, I think
>> that we should avoid the setting for performance.
>
>The "^1" syntax is quite useful if you're trying to reserve a CPU for
>use by another domain e.g. domain0, but don't want to otherwise restrict
>the guest.

"cpus" is parsed from left side, and the "^1" negates the values which 
was already parsed.  So "0-3,^1,1" and "0-3" are equivalent. 
The parsing of "cpus" cannot handle "negation" from a beginning because 
there is not a value to negate. 

But, I'm thinking that I want to implement Zhang's demand since I get 
your comment.  So I have idea as follows. 

  cpus = "0:,^1"

The "0:" means "0 or later".  How about it?


>We need to be able to deal with setting the affinity mask for a domain
>(that is replicated to all VCPUs) as for individual VCPUs. I assume your
>patch doesn't change the behaviour of the former?

Could you look at the following changest?

 http://xenbits.xensource.com/xen-unstable.hg/rev/5c3df1bded82


>BTW, it would also be nice to be able to specify CPUs by
>node.socket.core.thread as opposed to just enumerated CPU number. It
>should be possible to omit unused levels of the hierarchy, e.g. "0.3"
>could be used to refer to the 4th core of the first socket on a dual
>socket quad core machine.
>
>If you're looking for further improvements in this area, enable CPU
>groups to be defined and then allow domains/VCPUs to be assigned to a
>group.

I got interest for your suggestion.  Let me think for the time being.


Best regards,
 Kan



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