Re: [Xen-devel] [PATCH v8 13/15] xen: make grant resource limits per domain

[Juergen Gross <jgross@xxxxxxxx>]

On 21/09/17 13:31, Jan Beulich wrote:
>>>> On 21.09.17 at 09:53, <jgross@xxxxxxxx> wrote:
>> On 21/09/17 08:15, Jan Beulich wrote:
>>>>>> On 21.09.17 at 06:35, <jgross@xxxxxxxx> wrote:
>>>> On 20/09/17 17:35, Jan Beulich wrote:
>>>>>>>> On 20.09.17 at 14:44, <jgross@xxxxxxxx> wrote:
>>>>>> On 20/09/17 13:48, Jan Beulich wrote:
>>>>>>>>>> On 20.09.17 at 13:10, <jgross@xxxxxxxx> wrote:
>>>>>>>> I thought about a cap and TBH I'm not sure which would be sane to
>>>>>>>> apply. The global limits seem wrong, especially looking at patch 14:
>>>>>>>> those limits will be for dom0 only then. And dom0 won't need many
>>>>>>>> grant frames in the normal case...
>>>>>>>
>>>>>>> I've been thinking about this Dom0 aspect too over lunch. What
>>>>>>> about allowing the hardware domain to set its limit (only upwards
>>>>>>> of course) in setup_table(), without any upper bound enforced?
>>>>>>> This would free up the globals to be used as system wide limits
>>>>>>> again.
>>>>>>
>>>>>> This would be possible, of course.
>>>>>>
>>>>>> The question is whether the need to re-allocate the frame pointer arrays
>>>>>> is it worth.
>>>>>
>>>>> Input by others would be helpful...
>>>>
>>>> I think I'll go with additional cap boot parameters, so I don't think
>>>> we need dom0 to modify its own limits.
>>>
>>> So are we in agreement then that no new command line options
>>> are needed, and that hence the cap will be applicable to all
>>> domains (with Dom0 simply not having any other limit enforced
>>> on it)?
>>
>> Hmm, I meant this to be the other way round: having distinct parameters
>> for dom0 and the cap.
>>
>> In case you like it much better to merge them I won't argue over it.
> 
> Well, late yesterday evening it occurred to me that it would
> only be consistent to apply the same cap to all domains. That's
> in particular to not penalize a non-Dom0 hardware domain in
> comparison with Dom0 itself.

That's correct.

OTOH e.g. a cap of lets say 1024 grant frames but Dom0 configured to
4 only (why would it need more?) would make sense: the grant frame array
for Dom0 would need 32 bytes only instead of the 8kB for the 1024 frames
if the cap would be the configuration value for Dom0.


Juergen

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