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6593758: RFE: Enhance GC ergonomics to dynamically choose ParallelGCThreads

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Select number of GC threads dynamically based on heap usage and number of Java threads

Reviewed-by: johnc, ysr, jcoomes
This commit is contained in:
Jon Masamitsu 2011-08-09 10:16:01 -07:00
parent 098ed89645
commit 15070123fa
39 changed files with 1523 additions and 231 deletions
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42
hotspot/src/share/vm/memory/cardTableModRefBS.cpp
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@ -460,9 +460,43 @@ void CardTableModRefBS::non_clean_card_iterate_possibly_parallel(Space* sp,
OopsInGenClosure* cl,
CardTableRS* ct) {
if (!mr.is_empty()) {
int n_threads = SharedHeap::heap()->n_par_threads();
if (n_threads > 0) {
// Caller (process_strong_roots()) claims that all GC threads
// execute this call. With UseDynamicNumberOfGCThreads now all
// active GC threads execute this call. The number of active GC
// threads needs to be passed to par_non_clean_card_iterate_work()
// to get proper partitioning and termination.
//
// This is an example of where n_par_threads() is used instead
// of workers()->active_workers(). n_par_threads can be set to 0 to
// turn off parallelism. For example when this code is called as
// part of verification and SharedHeap::process_strong_roots() is being
// used, then n_par_threads() may have been set to 0. active_workers
// is not overloaded with the meaning that it is a switch to disable
// parallelism and so keeps the meaning of the number of
// active gc workers. If parallelism has not been shut off by
// setting n_par_threads to 0, then n_par_threads should be
// equal to active_workers. When a different mechanism for shutting
// off parallelism is used, then active_workers can be used in
// place of n_par_threads.
// This is an example of a path where n_par_threads is
// set to 0 to turn off parallism.
// [7] CardTableModRefBS::non_clean_card_iterate()
// [8] CardTableRS::younger_refs_in_space_iterate()
// [9] Generation::younger_refs_in_space_iterate()
// [10] OneContigSpaceCardGeneration::younger_refs_iterate()
// [11] CompactingPermGenGen::younger_refs_iterate()
// [12] CardTableRS::younger_refs_iterate()
// [13] SharedHeap::process_strong_roots()
// [14] G1CollectedHeap::verify()
// [15] Universe::verify()
// [16] G1CollectedHeap::do_collection_pause_at_safepoint()
//
int n_threads = SharedHeap::heap()->n_par_threads();
bool is_par = n_threads > 0;
if (is_par) {
#ifndef SERIALGC
assert(SharedHeap::heap()->n_par_threads() ==
SharedHeap::heap()->workers()->active_workers(), "Mismatch");
non_clean_card_iterate_parallel_work(sp, mr, cl, ct, n_threads);
#else // SERIALGC
fatal("Parallel gc not supported here.");
@ -489,6 +523,10 @@ void CardTableModRefBS::non_clean_card_iterate_possibly_parallel(Space* sp,
// change their values in any manner.
void CardTableModRefBS::non_clean_card_iterate_serial(MemRegion mr,
MemRegionClosure* cl) {
bool is_par = (SharedHeap::heap()->n_par_threads() > 0);
assert(!is_par ||
(SharedHeap::heap()->n_par_threads() ==
SharedHeap::heap()->workers()->active_workers()), "Mismatch");
for (int i = 0; i < _cur_covered_regions; i++) {
MemRegion mri = mr.intersection(_covered[i]);
if (mri.word_size() > 0) {