Hi,
On 22/03/2022 08:47, Bertrand Marquis wrote:
Hi Julien,
On 22 Mar 2022, at 09:35, Bertrand Marquis <bertrand.marq...@arm.com> wrote:
Hi Julien,
On 21 Mar 2022, at 18:44, Julien Grall <jul...@xen.org> wrote:
Hi Bertrand,
On 21/03/2022 17:19, Bertrand Marquis wrote:
On 21 Mar 2022, at 17:36, Julien Grall <jul...@xen.org> 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
I don't think we need this restriction. In fact, with this series it
will become more a problem because the cpupool ID will based on how we
parse the Device-Tree.
So for dom0, we need to specify explicitely the cpupool to be used.
- 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.
IMHO removing the second restriction is a lot more risky than removing
the first one.
Cheers,
--
Julien Grall
