linux-kernel - Re: [PATCH v2 2/2] of, numa: Fetch empty NUMA node ID from distance map

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Date:   Tue, 28 Sep 2021 09:59:25 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Rob Herring <robh@...nel.org>
Cc:     devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@...ts.cs.columbia.edu>, Marc Zyngier <maz@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, shan.gavin@...il.com
Subject: Re: [PATCH v2 2/2] of, numa: Fetch empty NUMA node ID from distance
 map

Hi Rob,

On 9/28/21 12:49 AM, Rob Herring wrote:
> On Mon, Sep 27, 2021 at 1:42 AM Gavin Shan <gshan@...hat.com> wrote:
>>
>> There is no device node for the empty NUMA node. However, the
>> corresponding NUMA node ID and distance map is still valid in
>> "numa-distance-map-v1" compatible device node.
>>
>> This fetches the NUMA node ID and distance map for these empty
>> NUMA node from "numa-distance-map-v1" compatible device node.
> 
> This is much nicer.
> 

Indeed, thanks for your suggestions :)

>> Signed-off-by: Gavin Shan <gshan@...hat.com>
>> ---
>>   drivers/of/of_numa.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/of/of_numa.c b/drivers/of/of_numa.c
>> index fe6b13608e51..5949829a1b00 100644
>> --- a/drivers/of/of_numa.c
>> +++ b/drivers/of/of_numa.c
>> @@ -111,6 +111,8 @@ static int __init of_numa_parse_distance_map_v1(struct device_node *map)
>>                          return -EINVAL;
>>                  }
>>
>> +               node_set(nodea, numa_nodes_parsed);
>> +
> 
> With this, couldn't we remove of_numa_parse_cpu_nodes() as the only
> thing it does is node_set()?
> 

I don't think so for couple of reasons:

(1) With problematic device-tree, the distance map node might be missed
     or incomplete. In this case, of_numa_parse_cpu_nodes() still helps.

(2) @numa_nodes_parsed is also updated when the memory nodes are iterated
     in of_numa_parse_memory_nodes() and numa_add_memblk().

So @numa_nodes_parsed, which is synchronized to @node_possible_map afterwards,
is the gathering output of CPU nodes, memory nodes and distance map node.

>>                  numa_set_distance(nodea, nodeb, distance);
>>
>>                  /* Set default distance of node B->A same as A->B */

Thanks,
Gavin