Re: [RFC v2 4/4] powerpc/papr_scm: Add cpu hotplug support for nvdimm pmu device

On Wed, May 26, 2021 at 12:56:58PM +0530, kajoljain wrote:

On 5/25/21 7:46 PM, Peter Zijlstra wrote:

quoted

On Tue, May 25, 2021 at 06:52:16PM +0530, Kajol Jain wrote:

quoted

quoted

It adds cpumask to designate a cpu to make HCALL to
collect the counter data for the nvdimm device and
update ABI documentation accordingly.

Result in power9 lpar system:
command:# cat /sys/devices/nmem0/cpumask
0

Is this specific to the papr thing, or should this be in generic nvdimm
code?

This code is not specific to papr device and we can move it to
generic nvdimm interface. But do we need to add some checks on whether
any arch/platform specific driver want that support or we can assume 
that this will be something needed by all platforms?

I'm a complete NVDIMM n00b, but to me it would appear they would have to
conform to the normal memory hierarchy and would thus always be
per-node.

Also, if/when deviation from this rule is observed, we can always
rework/extend this. For now I think it would make sense to have the
per-node ness of the thing expressed in the generic layer.