Subject: Re: [PATCH] powerpc/papr_scm: Update the NUMA distance table for the target node

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 30 Mar 2023 21:55:42 +0530

"Aneesh Kumar K.V" <[email-masked]> writes:

> platform device helper routines won't update the NUMA distance table
> while creating a platform device, even if the device is present on
> a NUMA node that doesn't have memory or CPU. This is especially true
> for pmem devices. If the target node of the pmem device is not online, we
> find the nearest online node to the device and associate the pmem
> device with that online node. To find the nearest online node, we should
> have the numa distance table updated correctly. Update the distance
> information during the device probe.
>
> distance_lookup_table value for distance_ref_points_depth = 2 before and after
> fix is below
> node 3 distance depth 0  - 0
> node 3 distance depth 1  - 0
> node 4 distance depth 0  - 4
> node 4 distance depth 1  - 2
> node 5 distance depth 0  - 5
> node 5 distance depth 1  - 1
>
> after fix
> node 3 distance depth 0  - 3
> node 3 distance depth 1  - 1
> node 4 distance depth 0  - 4
> node 4 distance depth 1  - 2
> node 5 distance depth 0  - 5
> node 5 distance depth 1  - 1
>
> Without the fix, the nearest numa node to the pmem device will be picked as 4.
> After the fix, we get the correct numa node which is 5.
>
> Fixes: da1115fdbd6e ("powerpc/nvdimm: Pick nearby online node if the device node is not online")
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/platforms/pseries/papr_scm.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index 2f8385523a13..5bef75714bd5 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -1428,6 +1428,10 @@ static int papr_scm_probe(struct platform_device *pdev)
>  		return -ENODEV;
>  	}
>  
> +	/*
> +	 * of platform device create won't update the numa distance table
> +	 */
> +	update_numa_distance(dn);
>  
>  	p = kzalloc(sizeof(*p), GFP_KERNEL);
>  	if (!p)
> -- 
> 2.39.2

This also requires export of update_numa_distance()

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index b44ce71917d7..16cfe56be05b 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -366,6 +366,7 @@ void update_numa_distance(struct device_node *node)
 	WARN(numa_distance_table[nid][nid] == -1,
 	     "NUMA distance details for node %d not provided\n", nid);
 }
+EXPORT_SYMBOL_GPL(update_numa_distance);
 
 /*
  * ibm,numa-lookup-index-table= {N, domainid1, domainid2, ..... domainidN}