On 26.04.2023 07:33, Henry Wang wrote: >> -----Original Message----- >> From: Jan Beulich <[email protected]> >> >>> + /* Get opposite way distance */ >>> + opposite = __node_distance(to, from); >>> + /* The default value in node_distance_map is NUMA_NO_DISTANCE >> */ >>> + if ( opposite == NUMA_NO_DISTANCE ) >> >> And the matrix you're reading from can't hold NUMA_NO_DISTANCE entries? >> I ask because you don't check this above; you only check against >> NUMA_LOCAL_DISTANCE. > > My understanding for the purpose of this part of code is to check if the > opposite > way distance has already been set, so we need to compare the opposite way > distance with the default value NUMA_NO_DISTANCE here. > > Back to your question, I can see your point of the question. However I don't > think > NUMA_NO_DISTANCE is a valid value to describe the node distance in the device > tree. This is because I hunted down the previous discussions and found [2] > about > we should try to keep consistent between the value used in device tree and > ACPI > tables. From the ACPI spec, 0xFF, i.e. NUMA_NO_DISTANCE means unreachable. > I think this is also the reason why NUMA_NO_DISTANCE can be used as the > default > value of the distance map, otherwise we won't have any value to use.
The [2] link you provided discusses NUMA_LOCAL_DISTANCE. Looking at Linux'es Documentation/devicetree/numa.txt, there's no mention of an upper bound on the distance values. It only says that on the diagonal entries should be 10 (i.e. matching ACPI, without really saying so). Jan
