Subject: Re: [RFC] powerpc/numa: Use VPHN based node ID information on shared processor LPARs

From: Michael Ellerman <[email-masked]>
Date: Wed, 14 Oct 2015 20:19:20 +1100

On Wed, 2015-10-14 at 14:32 +0530, Anshuman Khandual wrote:
> On shared processor LPARs, H_HOME_NODE_ASSOCIATIVITY hcall provides the
> dynamic virtual-physical mapping for any given processor. Currently we
> use VPHN node ID information only after getting either a PRRN or a VPHN
> event. But during boot time inside the function numa_setup_cpu, we still
> query the OF device tree for the node ID value which might be different
> than what can be fetched from the H_HOME_NODE_ASSOCIATIVITY hcall. In a
> scenario where there are no PRRN or VPHN event after boot, all node-cpu
> mapping will remain incorrect there after.
> 
> With this proposed change, numa_setup_cpu will try to override the OF
> device tree fetched node ID information with H_HOME_NODE_ASSOCIATIVITY
> hcall fetched node ID value. Right now shared processor property of the
> LPAR cannot be queried as VPA inializaion happens after numa_setup_cpu
> during boot time. So initmem_init function has been moved after ppc_md.
> setup_arch inside setup_arch during boot.

I would be *very* reluctant to change the order of initmem_init() vs
setup_arch().

At a minimum you'd need to go through every setup_arch() implementation and
carefully determine if the ordering of what it does matters vs initmem_init().
And then you'd need to test on every affected platform.

So I suggest you think of a different way to do it if at all possible.

cheers