1 /*
  2  * Copyright (c) 2018, 2021, Red Hat, Inc. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "precompiled.hpp"
 26 #include "gc/shared/gcArguments.hpp"
 27 #include "gc/shared/tlab_globals.hpp"
 28 #include "gc/shared/workerPolicy.hpp"
 29 #include "gc/shenandoah/shenandoahArguments.hpp"
 30 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
 31 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 32 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
 33 #include "runtime/globals_extension.hpp"
 34 #include "runtime/java.hpp"
 35 #include "utilities/defaultStream.hpp"
 36 
 37 void ShenandoahArguments::initialize() {
 38 #if !(defined AARCH64 || defined AMD64 || defined IA32)
 39   vm_exit_during_initialization("Shenandoah GC is not supported on this platform.");
 40 #endif
 41 
 42 #if 0 // leave this block as stepping stone for future platforms
 43   log_warning(gc)("Shenandoah GC is not fully supported on this platform:");
 44   log_warning(gc)("  concurrent modes are not supported, only STW cycles are enabled;");
 45   log_warning(gc)("  arch-specific barrier code is not implemented, disabling barriers;");
 46 
 47   FLAG_SET_DEFAULT(ShenandoahGCHeuristics,           "passive");
 48 
 49   FLAG_SET_DEFAULT(ShenandoahSATBBarrier,            false);
 50   FLAG_SET_DEFAULT(ShenandoahLoadRefBarrier,         false);
 51   FLAG_SET_DEFAULT(ShenandoahIUBarrier,              false);
 52   FLAG_SET_DEFAULT(ShenandoahCASBarrier,             false);
 53   FLAG_SET_DEFAULT(ShenandoahCloneBarrier,           false);
 54 
 55   FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers,     false);
 56 #endif
 57   if (UseLargePages) {
 58     size_t large_page_size = os::large_page_size();
 59     if ((align_up(MaxHeapSize, large_page_size) / large_page_size) < ShenandoahHeapRegion::MIN_NUM_REGIONS) {
 60       warning("Large pages size (" SIZE_FORMAT "K) is too large to afford page-sized regions, disabling uncommit",
 61               os::large_page_size() / K);
 62       FLAG_SET_DEFAULT(ShenandoahUncommit, false);
 63     }
 64   }
 65 
 66   // Enable NUMA by default. While Shenandoah is not NUMA-aware, enabling NUMA makes
 67   // storage allocation code NUMA-aware.
 68   if (FLAG_IS_DEFAULT(UseNUMA)) {
 69     FLAG_SET_DEFAULT(UseNUMA, true);
 70   }
 71 
 72   // Set up default number of concurrent threads. We want to have cycles complete fast
 73   // enough, but we also do not want to steal too much CPU from the concurrently running
 74   // application. Using 1/4 of available threads for concurrent GC seems a good
 75   // compromise here.
 76   bool ergo_conc = FLAG_IS_DEFAULT(ConcGCThreads);
 77   if (ergo_conc) {
 78     FLAG_SET_DEFAULT(ConcGCThreads, MAX2(1, os::initial_active_processor_count() / 4));
 79   }
 80 
 81   if (ConcGCThreads == 0) {
 82     vm_exit_during_initialization("Shenandoah expects ConcGCThreads > 0, check -XX:ConcGCThreads=#");
 83   }
 84 
 85   // Set up default number of parallel threads. We want to have decent pauses performance
 86   // which would use parallel threads, but we also do not want to do too many threads
 87   // that will overwhelm the OS scheduler. Using 1/2 of available threads seems to be a fair
 88   // compromise here. Due to implementation constraints, it should not be lower than
 89   // the number of concurrent threads.
 90   bool ergo_parallel = FLAG_IS_DEFAULT(ParallelGCThreads);
 91   if (ergo_parallel) {
 92     FLAG_SET_DEFAULT(ParallelGCThreads, MAX2(1, os::initial_active_processor_count() / 2));
 93   }
 94 
 95   if (ParallelGCThreads == 0) {
 96     vm_exit_during_initialization("Shenandoah expects ParallelGCThreads > 0, check -XX:ParallelGCThreads=#");
 97   }
 98 
 99   // Make sure ergonomic decisions do not break the thread count invariants.
100   // This may happen when user overrides one of the flags, but not the other.
101   // When that happens, we want to adjust the setting that was set ergonomically.
102   if (ParallelGCThreads < ConcGCThreads) {
103     if (ergo_conc && !ergo_parallel) {
104       FLAG_SET_DEFAULT(ConcGCThreads, ParallelGCThreads);
105     } else if (!ergo_conc && ergo_parallel) {
106       FLAG_SET_DEFAULT(ParallelGCThreads, ConcGCThreads);
107     } else if (ergo_conc && ergo_parallel) {
108       // Should not happen, check the ergonomic computation above. Fail with relevant error.
109       vm_exit_during_initialization("Shenandoah thread count ergonomic error");
110     } else {
111       // User settings error, report and ask user to rectify.
112       vm_exit_during_initialization("Shenandoah expects ConcGCThreads <= ParallelGCThreads, check -XX:ParallelGCThreads, -XX:ConcGCThreads");
113     }
114   }
115 
116   if (ShenandoahRegionSampling && FLAG_IS_DEFAULT(PerfDataMemorySize)) {
117     // When sampling is enabled, max out the PerfData memory to get more
118     // Shenandoah data in, including Matrix.
119     FLAG_SET_DEFAULT(PerfDataMemorySize, 2048*K);
120   }
121 
122 #ifdef COMPILER2
123   // Shenandoah cares more about pause times, rather than raw throughput.
124   if (FLAG_IS_DEFAULT(UseCountedLoopSafepoints)) {
125     FLAG_SET_DEFAULT(UseCountedLoopSafepoints, true);
126     if (FLAG_IS_DEFAULT(LoopStripMiningIter)) {
127       FLAG_SET_DEFAULT(LoopStripMiningIter, 1000);
128     }
129   }
130 #ifdef ASSERT
131   // C2 barrier verification is only reliable when all default barriers are enabled
132   if (ShenandoahVerifyOptoBarriers &&
133           (!FLAG_IS_DEFAULT(ShenandoahSATBBarrier)            ||
134            !FLAG_IS_DEFAULT(ShenandoahLoadRefBarrier)         ||
135            !FLAG_IS_DEFAULT(ShenandoahIUBarrier)              ||
136            !FLAG_IS_DEFAULT(ShenandoahCASBarrier)             ||
137            !FLAG_IS_DEFAULT(ShenandoahCloneBarrier)
138           )) {
139     warning("Unusual barrier configuration, disabling C2 barrier verification");
140     FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
141   }
142 #else
143   guarantee(!ShenandoahVerifyOptoBarriers, "Should be disabled");
144 #endif // ASSERT
145 #endif // COMPILER2
146 
147   // Record more information about previous cycles for improved debugging pleasure
148   if (FLAG_IS_DEFAULT(LogEventsBufferEntries)) {
149     FLAG_SET_DEFAULT(LogEventsBufferEntries, 250);
150   }
151 
152   if ((InitialHeapSize == MaxHeapSize) && ShenandoahUncommit) {
153     log_info(gc)("Min heap equals to max heap, disabling ShenandoahUncommit");
154     FLAG_SET_DEFAULT(ShenandoahUncommit, false);
155   }
156 
157   // If class unloading is disabled, no unloading for concurrent cycles as well.
158   if (!ClassUnloading) {
159     FLAG_SET_DEFAULT(ClassUnloadingWithConcurrentMark, false);
160   }
161 
162   // TLAB sizing policy makes resizing decisions before each GC cycle. It averages
163   // historical data, assigning more recent data the weight according to TLABAllocationWeight.
164   // Current default is good for generational collectors that run frequent young GCs.
165   // With Shenandoah, GC cycles are much less frequent, so we need we need sizing policy
166   // to converge faster over smaller number of resizing decisions.
167   if (FLAG_IS_DEFAULT(TLABAllocationWeight)) {
168     FLAG_SET_DEFAULT(TLABAllocationWeight, 90);
169   }
170 }
171 
172 size_t ShenandoahArguments::conservative_max_heap_alignment() {
173   size_t align = ShenandoahMaxRegionSize;
174   if (UseLargePages) {
175     align = MAX2(align, os::large_page_size());
176   }
177   return align;
178 }
179 
180 void ShenandoahArguments::initialize_alignments() {
181   // Need to setup sizes early to get correct alignments.
182   MaxHeapSize = ShenandoahHeapRegion::setup_sizes(MaxHeapSize);
183 
184   // This is expected by our algorithm for ShenandoahHeap::heap_region_containing().
185   size_t align = ShenandoahHeapRegion::region_size_bytes();
186   if (UseLargePages) {
187     align = MAX2(align, os::large_page_size());
188   }
189   SpaceAlignment = align;
190   HeapAlignment = align;
191 }
192 
193 CollectedHeap* ShenandoahArguments::create_heap() {
194   return new ShenandoahHeap(new ShenandoahCollectorPolicy());
195 }