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 12:22:08 -0500
From:   Rob Herring <robh@...nel.org>
To:     Gavin Shan <gshan@...hat.com>
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

On Mon, Sep 27, 2021 at 6:59 PM Gavin Shan <gshan@...hat.com> wrote:
>
> 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.

It's not the kernel's job to validate the DT (if it was, it is doing a
terrible job). I would suggest writing some checks for dtc if we're
worried about correctness. (The schemas don't work too well for cross
node checks.)

> (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.

Is it valid to have node id's that are not in the distance map?

Rob