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8244376: possibly stale comment above "struct SharedGlobals" in synchronizer.cpp

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Reviewed-by: hseigel, dholmes
This commit is contained in:
Daniel D. Daugherty 2020-11-16 14:10:08 +00:00
parent c85c9ad1f1
commit 1d7ed03d5c
1 changed files with 0 additions and 18 deletions
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src/hotspot/share/runtime/synchronizer.cpp
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@ -720,24 +720,6 @@ void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
// -----------------------------------------------------------------------------
// Hash Code handling
//
// Performance concern:
// OrderAccess::storestore() calls release() which at one time stored 0
// into the global volatile OrderAccess::dummy variable. This store was
// unnecessary for correctness. Many threads storing into a common location
// causes considerable cache migration or "sloshing" on large SMP systems.
// As such, I avoided using OrderAccess::storestore(). In some cases
// OrderAccess::fence() -- which incurs local latency on the executing
// processor -- is a better choice as it scales on SMP systems.
//
// See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
// a discussion of coherency costs. Note that all our current reference
// platforms provide strong ST-ST order, so the issue is moot on IA32,
// x64, and SPARC.
//
// As a general policy we use "volatile" to control compiler-based reordering
// and explicit fences (barriers) to control for architectural reordering
// performed by the CPU(s) or platform.
struct SharedGlobals {
char _pad_prefix[OM_CACHE_LINE_SIZE];