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RE: [PATCH v3 07/22] xen/device-tree: Read NUMA node distance from Device Tree 'distance-map'
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Hirokazu Takahashi <taka@xxxxxxxxxxxxx>
- Date: Mon, 22 Jun 2026 08:49:15 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 22 Jun 2026 08:49:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHc/8BKTM3OweAnP0qpxuJk/PcKwrZFkCwAgAIwFqCAAn5KgIAACM8Q
- Thread-topic: [PATCH v3 07/22] xen/device-tree: Read NUMA node distance from Device Tree 'distance-map'
Hello,
> >>> + entry_count = len / sizeof(__be32);
> >>
> >> Nit: Better sizeof(<expression>).
> >
> > Is the following line better?
> > entry_count = len / sizeof(*matrix);
>
> Yes.
Okay.
> >>> + const unsigned int nr_nodes = last_node(node_online_map) + 1U;
> >>> +
> >>> + if ( from >= nr_nodes || to >= nr_nodes )
> >>> + return from == to ? LOCAL_DISTANCE : REMOTE_DISTANCE;
> >>
> >> What if either node is NUMA_NO_NODE?
> >
> > This behavior comes from the Linux kernel. It seems it exists as a defensive
> > fallback to keep the system running even with invalid or unassigned nodes.
> >
> > Do you think it is better to make it return 0xFF instead whenever any
> > out-of-bounds node or NUMA_NO_NODE is passed?
>
> Whether it's 0xff or REMOTE_DISTANCE I'm not quite sure. But it certainly
> shouldn't be LOCAL_DISTANCE.
Yes, that makes sense.
> >>> + for ( i = 0U; i < nr_nodes; i++ )
> >>> + for ( j = 0U; j < nr_nodes; j++ )
> >>
> >> Why the U suffixes?
> >
> > I added the U suffixes because variables i and j are unsigned types.
> > If a plain 0 is preferred here, I will remove them.
>
> They, even if only slightly, hamper readability. We tend to add them only
> when there actually is a need.
Okay.
Hirokazu Takahashi.
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