Fix depth field bug and resize() function in hierarchical barrier
This is a follow up to the hierarchy cleanup patch.
Added some clarifying comments to hierarchy_info.
Fixed a bug with the depth field not being updated cleanly during a resize.
Fixed resize to first check capacity as determined by maxLevels before actually doing the full resize.
Differential Revision: http://reviews.llvm.org/D12562
llvm-svn: 247333
diff --git a/openmp/runtime/src/kmp_affinity.h b/openmp/runtime/src/kmp_affinity.h
index 75f21ed..0385307 100644
--- a/openmp/runtime/src/kmp_affinity.h
+++ b/openmp/runtime/src/kmp_affinity.h
@@ -119,15 +119,21 @@
}
-/** A structure for holding machine-specific hierarchy info to be computed once at init. */
+/** A structure for holding machine-specific hierarchy info to be computed once at init.
+ This structure represents a mapping of threads to the actual machine hierarchy, or to
+ our best guess at what the hierarchy might be, for the purpose of performing an
+ efficient barrier. In the worst case, when there is no machine hierarchy information,
+ it produces a tree suitable for a barrier, similar to the tree used in the hyper barrier. */
class hierarchy_info {
public:
/** Good default values for number of leaves and branching factor, given no affinity information.
Behaves a bit like hyper barrier. */
static const kmp_uint32 maxLeaves=4;
static const kmp_uint32 minBranch=4;
- /** Typical levels are threads/core, cores/package or socket, packages/node, nodes/machine,
- etc. We don't want to get specific with nomenclature */
+ /** Number of levels in the hierarchy. Typical levels are threads/core, cores/package
+ or socket, packages/node, nodes/machine, etc. We don't want to get specific with
+ nomenclature. When the machine is oversubscribed we add levels to duplicate the
+ hierarchy, doubling the thread capacity of the hierarchy each time we add a level. */
kmp_uint32 maxLevels;
/** This is specifically the depth of the machine configuration hierarchy, in terms of the
@@ -227,6 +233,7 @@
}
+ // Resize the hierarchy if nproc changes to something larger than before
void resize(kmp_uint32 nproc)
{
kmp_int8 bool_result = KMP_COMPARE_AND_STORE_ACQ8(&resizing, 0, 1);
@@ -237,13 +244,23 @@
KMP_DEBUG_ASSERT(bool_result!=0);
KMP_DEBUG_ASSERT(nproc > base_num_threads);
- // Calculate new max_levels
+ // Calculate new maxLevels
kmp_uint32 old_sz = skipPerLevel[depth-1];
- kmp_uint32 incs = 0, old_maxLevels= maxLevels;
+ kmp_uint32 incs = 0, old_maxLevels = maxLevels;
+ // First see if old maxLevels is enough to contain new size
+ for (kmp_uint32 i=depth; i<maxLevels && nproc>old_sz; ++i) {
+ skipPerLevel[i] = 2*skipPerLevel[i-1];
+ old_sz *= 2;
+ depth++;
+ }
+ if (nproc <= old_sz) // enough space already
+ return;
+ // Not enough space, need to expand hierarchy
while (nproc > old_sz) {
old_sz *=2;
incs++;
- }
+ depth++;
+ }
maxLevels += incs;
// Resize arrays