Re: [PATCH] cpupools: retry cpupool-destroy if domain in cpupool is dying

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

On 07.05.2014 15:10, George Dunlap wrote:
> On Wed, May 7, 2014 at 8:52 AM, Juergen Gross
> <juergen.gross@ts.fujitsu.com> wrote:
>> When a cpupool is destroyed just after the last domain has been stopped the
>> domain might already be removed from the cpupool without having decremented
>> the domain count of the cpupool. This will result in rejection of the
>> cpupool-destroy operation.
>
> I'm a bit confused.  What's the sched_move_domain() for, then?  If
> we're going to handle "dying domains" by doing a retry, could we just
> get rid of it?

The sched_move_domain() is still needed for cases where a domain stays
dying for a longer time, e.g. when a dom0 process is still referencing
some of it's memory pages. This may be a rare situation, but being unable
to use a physical cpu for another cpupool just because of this case is
worse than this little piece of code, IMO.


Juergen

>
>   -George
>
>> It is easy to detect this situation and to return EAGAIN in this case which
>> is already handled in libxc by doing a retry.
>>
>> Signed-off-by: Juergen Gross <juergen.gross@ts.fujitsu.com>
>> ---
>>   xen/common/cpupool.c |    2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
>> index 4a0e569..ac833f0 100644
>> --- a/xen/common/cpupool.c
>> +++ b/xen/common/cpupool.c
>> @@ -348,6 +348,8 @@ static int cpupool_unassign_cpu(struct cpupool *c, unsigned int cpu)
>>               cpupool0->n_dom++;
>>           }
>>           rcu_read_unlock(&domlist_read_lock);
>> +        if ( (c->n_dom > 0) && !ret )
>> +            ret = -EAGAIN;
>>           if ( ret )
>>               goto out;
>>       }
>> --
>> 1.7.10.4
>>
>>
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>
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>
>


-- 
Juergen Gross                 Principal Developer Operating Systems
PSO PM&D ES&S SWE OS6                  Telephone: +49 (0) 89 62060 2932
Fujitsu                                   e-mail: juergen.gross@ts.fujitsu.com
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D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html