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Re: [PATCH v3 4/6] xen/cpupool: Create different cpupools at boot time
- To: Julien Grall <julien@xxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Tue, 22 Mar 2022 08:47:16 +0000
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- Cc: Luca Fancellu <Luca.Fancellu@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>
- Delivery-date: Tue, 22 Mar 2022 08:47:40 +0000
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- Thread-topic: [PATCH v3 4/6] xen/cpupool: Create different cpupools at boot time
Hi Julien,
> On 22 Mar 2022, at 09:35, Bertrand Marquis <bertrand.marquis@xxxxxxx> wrote:
>
> Hi Julien,
>
>> On 21 Mar 2022, at 18:44, Julien Grall <julien@xxxxxxx> wrote:
>>
>> Hi Bertrand,
>>
>> On 21/03/2022 17:19, Bertrand Marquis wrote:
>>>> On 21 Mar 2022, at 17:36, Julien Grall <julien@xxxxxxx> wrote:
>>>>> So I don’t know why on x86 we must have cpu0 in cpupool0, maybe x86
>>>>> maintainer have more knowledge about that and
>>>>> I can put a comment here.
>>>>
>>>> On Arm, we are not yet supporting all the CPU features that x86 supports
>>>> (e.g. CPU hotplug, suspend/resume...). So I a am bit concerned that the
>>>> restriction is just not there yet (or possibly hidden).
>>>>
>>>> Therefore, before lifting the restriction on Arm (and other arch), I would
>>>> like us to understand why it is necessary on x86.
>>>>
>>>> We may not have the answer quickly, so is it going to be a problem to keep
>>>> the restriction on Arm?
>>> I am ok to keep the limitation to have dom0 always running on cpu0.
>>> Only limitation I can see is that on a big little system, dom0 needs to
>>> stay on the type of core of the first booted core.
>>
>> Where does this limitation come from?
>
> If dom0 must run on core0 and core0 is Little then you cannot build a system
> where dom0 is running on big cores.
> If the limitation is not there, you can build such a configuration without
> any dependency to the boot core type.
This might not be completely clear so let me rephrase:
In the current system:
- dom0 must run on cpupool-0
- cpupool-0 must contain the boot core
- consequence: dom0 must run on the boot core
If boot core is little, you cannot build as system where dom0 runs only on the
big cores.
Removing the second limitation (which is not required on arm) is making it
possible.
Regards
Bertrand
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