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Re: [PATCH v6 5/6] arm/dom0less: assign dom0less guests to cpupools


  • To: Luca Fancellu <Luca.Fancellu@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Fri, 8 Apr 2022 12:24:43 +0200
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Fri, 08 Apr 2022 10:24:58 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 08.04.2022 11:39, Luca Fancellu wrote:
> 
> 
>> On 8 Apr 2022, at 10:10, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 08.04.2022 10:45, Luca Fancellu wrote:
>>> @@ -106,6 +106,8 @@ struct xen_domctl_createdomain {
>>>     /* Per-vCPU buffer size in bytes.  0 to disable. */
>>>     uint32_t vmtrace_size;
>>>
>>> +    uint32_t cpupool_id;
>>
>> This could do with a comment explaining default behavior. In particular
>> I wonder what 0 means: Looking at cpupool_destroy() I can't see that it
>> would be impossible to delete pool 0 (but there may of course be
>> reasons elsewhere, e.g. preventing pool 0 to ever go empty) - Jürgen?
>> Yet if pool 0 can be removed, zero being passed in here should imo not
>> lead to failure of VM creation. Otoh I understand that this would
>> already happen ahead of your change, preventing of which would
>> apparently possible only via passing CPUPOOLID_NONE here.
> 
> Pool-0 can’t be emptied because Dom0 is sitting there (the patch is modifying
> cpupool_id only for DomUs).

But we're talking about dom0less as per the subject of the patch here.

> I thought the name was self explanatory, but if I have to put a comment, would
> It work something like that:
> 
> /* Cpupool id where the domain will be assigned on creation */

I don't view this kind of comment as necessary. I was really after
calling out default behavior, along the lines of "0 to disable" that
you can see in patch context.

Jan




 


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