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Re: [RFC PATCH 0/2] Boot time cpupools



On 17/11/2021 11:16, Bertrand Marquis wrote:
Hi Julien,

Hi,

On 17 Nov 2021, at 10:26, Julien Grall <julien@xxxxxxx> wrote:

Hi Luca,

On 17/11/2021 09:57, Luca Fancellu wrote:
Currently Xen creates a default cpupool0 that contains all the cpu brought up
during boot and it assumes that the platform has only one kind of CPU.
This assumption does not hold on big.LITTLE platform, but putting different
type of CPU in the same cpupool can result in instability and security issues
for the domains running on the pool.

I agree that you can't move a LITTLE vCPU to a big pCPU. However...

For this reason this serie introduces an architecture specific way to create
different cpupool at boot time, this is particularly useful on ARM big.LITTLE
platform where there might be the need to have different cpupools for each type
of core, but also systems using NUMA can have different cpu pool for each node.

... from my understanding, all the vCPUs of a domain have to be in the same 
cpupool. So with this approach it is not possible:
   1) to have a mix of LITTLE and big vCPUs in the domain
   2) to create a domain spanning across two NUMA nodes

So I think we need to make sure that any solutions we go through will not 
prevent us to implement those setups.

The point of this patch is to make all cores available without breaking the 
current behaviour of existing system.

I might be missing some context here. By breaking current behavior, do you mean user that may want to add "hmp-unsafe" on the command line?

Cheers,

--
Julien Grall



 


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