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

["Zhang, Jingke" <jingke.zhang@xxxxxxxxx>]

Masaki Kanno wrote:
> 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?
> 

Hi Kanno,
    I think a "non-boundary" range may be needed to define the
expression. How about this:
    "x-", means from CPUx to the last CPU. For example, "0-" means 0 or
later.
    "-x", means from CPU0 to CPUx, for example, "-3" means "0,1,2,3". 
    Thank you!

> 
>> 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



Thanks,
Zhang Jingke

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