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CP-311531: handle both 32-bit and 64-bit unreachable distances in the NUMA matrix #6897

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CP-311531: handle both 32-bit and 64-bit unreachable distances in the NUMA matrix #6897

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25 changes: 15 additions & 10 deletions ocaml/xenopsd/lib/topology.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -146,11 +146,18 @@ module NUMA = struct
let compare (Node a) (Node b) = compare a b
end)

(* -1 in 32 bits *)
let unreachable_distance = 0xFFFFFFFF
let max_valid_distance = 0xFF

let self_distance = 10

let is_unreachable d = d > max_valid_distance || d < 0

let () =
(* 32-bit *)
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@lindig lindig Feb 9, 2026

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I am a bit surprised that when this is read from Xen and converted to an int, that it is not sign extended and thus would be -1 in all cases. it seems we are currently treating the return value as an unsigned number.

assert (is_unreachable 0xFFFFFFFF) ;
(* 64-bit, the value returned by Xen could change *)
assert (is_unreachable ~-1)

(* no mutation is exposed in the interface, therefore this is immutable *)
type t = {
distances: int array array
Expand Down Expand Up @@ -198,10 +205,10 @@ module NUMA = struct
seq_range 0 (Array.length d)
|> Seq.filter_map (fun i ->
let self = d.(i).(i) in
if self <> unreachable_distance then
Some i
else
if is_unreachable self then
None
else
Some i
)
in
let numa_nodes = Seq.length valid_nodes in
Expand Down Expand Up @@ -235,7 +242,7 @@ module NUMA = struct
Array.iteri
(fun i node ->
let self = distances.(node).(node) in
if self <> unreachable_distance then
if not (is_unreachable self) then
node_cpus.(node) <- CPUSet.add i node_cpus.(node)
)
cpu_to_node ;
Expand All @@ -254,10 +261,8 @@ module NUMA = struct
|> Array.to_seqi
|> Seq.for_all (fun (i, row) ->
let d = distances.(i).(i) in
(d = unreachable_distance || d = self_distance)
&& Array.for_all
(fun d -> d >= self_distance || d = unreachable_distance)
row
(is_unreachable d || d = self_distance)
&& Array.for_all (fun d -> d >= self_distance || is_unreachable d) row
)
in

Expand Down
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