Re: [PATCH] xl cpupool-numa-split: reduce number of Dom0 vcpus

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 02/15/11 20:27, Ian Jackson wrote:
> Juergen Gross writes ("Re: [Xen-devel] [PATCH] xl cpupool-numa-split: reduce number of Dom0 vcpus"):
>> I added a failure exit if not all required vcpus are offlined.
>
> Thanks.  But, is this test correct ?
>
>> +        if (info.vcpu_online == n) {
>> +            break;
>> +        }
>
> Is it possible for the online map to have n cpus in it, but for them
> to be the wrong n cpus ?

The number of online vcpus is important, not which vcpus.
In a strange case it could lead to a wrong number of online vcpus, if the
number was correct in the beginning and e.g. vcpu 0 was offline and
offlining the last vcpu fails. But I don't think this would be a huge
problem, as offlining the vcpus is just a optimization measure.

>
> What if two copies of this code run concurrently ?  (Perhaps in 4.2 we
> will need to add a lock?)

The result of both copies should be the same, as it is depending on the
machine configuration only.
And we are speaking of a global machine configuration action. This would mean
two administrators are configuring the same machine without knowing what the
other is doing. Seems to be a very strange scenario. A possible failure
(meaning: not reaching the desired configuration, but no crashing) should be
regarded as acceptable in this case.


Juergen

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Juergen Gross                 Principal Developer Operating Systems
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