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

[Julien Grall <julien@xxxxxxx>]

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