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[TE/Topology] Enhance PCI distance calculation by considering NUMA node affinity #1086

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[TE/Topology] Enhance PCI distance calculation by considering NUMA node affinity #1086

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14 changes: 14 additions & 0 deletions mooncake-transfer-engine/src/topology.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,20 @@ static int getPciDistance(const char *bus1, const char *bus2) {
distance += (*ptr2 == '/');
}

// If both devices report the same valid NUMA node, treat them as
// one hop closer by subtracting 1 from the computed distance.
int numa1 = -1;
int numa2 = -1;
char numa_path[PATH_MAX];
snprintf(numa_path, sizeof(numa_path), "%s/numa_node", path1);
std::ifstream(numa_path) >> numa1;
snprintf(numa_path, sizeof(numa_path), "%s/numa_node", path2);
std::ifstream(numa_path) >> numa2;
Comment on lines +162 to +165
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@gemini-code-assist gemini-code-assist bot Nov 20, 2025

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high

The snprintf calls to construct the numa_node path could result in a truncated path if the source path (path1 or path2) is very long. This would cause the file read to fail silently, and the NUMA affinity optimization would not be applied. It's safer to check the return value of snprintf to detect and handle potential truncation.

Additionally, the logic to read the NUMA node is duplicated. While the suggestion below fixes the immediate safety issue, I'd recommend refactoring this logic into a helper function to improve code maintainability and readability in a follow-up.

Suggested change
snprintf(numa_path, sizeof(numa_path), "%s/numa_node", path1);
std::ifstream(numa_path) >> numa1;
snprintf(numa_path, sizeof(numa_path), "%s/numa_node", path2);
std::ifstream(numa_path) >> numa2;
int ret = snprintf(numa_path, sizeof(numa_path), "%s/numa_node", path1);
if (ret > 0 && static_cast<size_t>(ret) < sizeof(numa_path)) {
std::ifstream(numa_path) >> numa1;
}
ret = snprintf(numa_path, sizeof(numa_path), "%s/numa_node", path2);
if (ret > 0 && static_cast<size_t>(ret) < sizeof(numa_path)) {
std::ifstream(numa_path) >> numa2;
}


if (numa1 != -1 && numa1 == numa2 && distance > 0) {
distance -= 1;
}

return distance;
}

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