Subject: Re: [PATCH] powerpc/numa: Restrict possible nodes based on platform

From: Srikar Dronamraju <[email-masked]>
Date: Tue, 7 Jul 2020 14:12:03 +0530

* Michael Ellerman <[email-masked]> [2020-07-07 15:02:17]:

> Srikar Dronamraju <[email-masked]> writes:
> > As per PAPR, there are 2 device tree property
> > ibm,max-associativity-domains (which defines the maximum number of
> > domains that the firmware i.e PowerVM can support) and
> > ibm,current-associativity-domains (which defines the maximum number of
> > domains that the platform can support). Value of
> > ibm,max-associativity-domains property is always greater than or equal
> > to ibm,current-associativity-domains property.
> 
> Where is it documented?
> 
> It's definitely not in LoPAPR.
> 

https://openpowerfoundation.org/wp-content/uploads/2020/07/LoPAR-20200611.pdf
Page number 833.

which says 
ibm,current-associativity-domains”
	property name to define the current number of associativity
	domains for this platform.
	prop-encoded-array: An associativity list such that all values are
	the number of unique values that the current platform supports
	in that location. The associativity list consisting of a number of
	entries integer (N) encoded as with encode-int followed by N
	integers encoded as with encode-int each representing current
	number of unique associativity domains the platform supports at
	that level.

> > Powerpc currently uses ibm,max-associativity-domains  property while
> > setting the possible number of nodes. This is currently set at 32.
> > However the possible number of nodes for a platform may be significantly
> > less. Hence set the possible number of nodes based on
> > ibm,current-associativity-domains property.
> >
> > $ lsprop /proc/device-tree/rtas/ibm,*associ*-domains
> > /proc/device-tree/rtas/ibm,current-associativity-domains
> > 		 00000005 00000001 00000002 00000002 00000002 00000010
> > /proc/device-tree/rtas/ibm,max-associativity-domains
> > 		 00000005 00000001 00000008 00000020 00000020 00000100
> >
> > $ cat /sys/devices/system/node/possible ##Before patch
> > 0-31
> >
> > $ cat /sys/devices/system/node/possible ##After patch
> > 0-1
> >
> > Note the maximum nodes this platform can support is only 2 but the
> > possible nodes is set to 32.
> 
> But what about LPM to a system with more nodes?
> 

I have very less info on LPM, so I checked with Nathan Lynch before posting
and as per Nathan in the current design of LPM, Linux wouldn't use the new
node numbers. 

-- 
Thanks and Regards
Srikar Dronamraju