[Openmp-commits] [PATCH] D61796: Fix hwloc topology traversal code unable to handle situation where L2 cache is common for the packages

Paul Osmialowski via Phabricator via Openmp-commits openmp-commits at lists.llvm.org
Fri May 10 11:48:06 PDT 2019

pawosm01 created this revision.
Herald added subscribers: openmp-commits, jdoerfert.
Herald added a project: OpenMP.

Currently cores within package that share the same L2 cache are grouped together. The current logic behind this assumes that the L2 cache is always at deeper (or the same) level than the package itself. In case when L2 cache is common for all packages (and the packages are at deeper level than L2 cache) the whole of the further topology discovery fails to find any computational units resulting in following assertion:

Assertion failure at kmp_affinity.cpp(715): nActiveThreads == __kmp_avail_proc.
OMP: Error #13: Assertion failure at kmp_affinity.cpp(715).

This patch adds a bit of a logic that prevents such situation from occurring.

  rOMP OpenMP



Index: runtime/src/kmp_affinity.cpp
--- runtime/src/kmp_affinity.cpp
+++ runtime/src/kmp_affinity.cpp
@@ -530,7 +530,7 @@
 static int __kmp_hwloc_check_numa() {
   hwloc_topology_t &tp = __kmp_hwloc_topology;
   hwloc_obj_t hT, hC, hL, hN, hS; // hwloc objects (pointers to)
-  int depth;
+  int depth, l2cache_depth, package_depth;
   // Get some PU
   hT = hwloc_get_obj_by_type(tp, HWLOC_OBJ_PU, 0);
@@ -548,8 +548,10 @@
+  package_depth = hwloc_get_type_depth(tp, HWLOC_OBJ_PACKAGE);
+  l2cache_depth = hwloc_get_cache_type_depth(tp, 2, HWLOC_OBJ_CACHE_UNIFIED);
   // check tile, get object by depth because of multiple caches possible
-  depth = hwloc_get_cache_type_depth(tp, 2, HWLOC_OBJ_CACHE_UNIFIED);
+  depth = (l2cache_depth < package_depth) ? package_depth : l2cache_depth;
   hL = hwloc_get_ancestor_obj_by_depth(tp, depth, hT);
   hC = NULL; // not used, but reset it here just in case
   if (hL != NULL &&

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