1 /*
   2  * Copyright (c) 2018, 2019, 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.inline.hpp"
  27 #include "gc/shenandoah/shenandoahArguments.hpp"
  28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
  29 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  30 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
  31 #include "utilities/defaultStream.hpp"
  32 
  33 void ShenandoahArguments::initialize() {
  34 #if !(defined AARCH64 || defined AMD64 || defined IA32)
  35   vm_exit_during_initialization("Shenandoah GC is not supported on this platform.");
  36 #endif
  37 
  38 #if 0 // leave this block as stepping stone for future platforms
  39   log_warning(gc)("Shenandoah GC is not fully supported on this platform:");
  40   log_warning(gc)("  concurrent modes are not supported, only STW cycles are enabled;");
  41   log_warning(gc)("  arch-specific barrier code is not implemented, disabling barriers;");
  42 
  43   FLAG_SET_DEFAULT(ShenandoahGCHeuristics,           "passive");
  44 
  45   FLAG_SET_DEFAULT(ShenandoahSATBBarrier,            false);
  46   FLAG_SET_DEFAULT(ShenandoahLoadRefBarrier,         false);
  47   FLAG_SET_DEFAULT(ShenandoahStoreValEnqueueBarrier, false);
  48   FLAG_SET_DEFAULT(ShenandoahCASBarrier,             false);
  49   FLAG_SET_DEFAULT(ShenandoahCloneBarrier,           false);
  50 
  51   FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers,     false);
  52 #endif
  53 
  54   if (UseLargePages && (MaxHeapSize / os::large_page_size()) < ShenandoahHeapRegion::MIN_NUM_REGIONS) {
  55     warning("Large pages size (" SIZE_FORMAT "K) is too large to afford page-sized regions, disabling uncommit",
  56             os::large_page_size() / K);
  57     FLAG_SET_DEFAULT(ShenandoahUncommit, false);
  58   }
  59 
  60   // Enable NUMA by default. While Shenandoah is not NUMA-aware, enabling NUMA makes
  61   // storage allocation code NUMA-aware.
  62   if (FLAG_IS_DEFAULT(UseNUMA)) {
  63     FLAG_SET_DEFAULT(UseNUMA, true);
  64   }
  65 
  66   // Set up default number of concurrent threads. We want to have cycles complete fast
  67   // enough, but we also do not want to steal too much CPU from the concurrently running
  68   // application. Using 1/4 of available threads for concurrent GC seems a good
  69   // compromise here.
  70   bool ergo_conc = FLAG_IS_DEFAULT(ConcGCThreads);
  71   if (ergo_conc) {
  72     FLAG_SET_DEFAULT(ConcGCThreads, MAX2(1, os::initial_active_processor_count() / 4));
  73   }
  74 
  75   if (ConcGCThreads == 0) {
  76     vm_exit_during_initialization("Shenandoah expects ConcGCThreads > 0, check -XX:ConcGCThreads=#");
  77   }
  78 
  79   // Set up default number of parallel threads. We want to have decent pauses performance
  80   // which would use parallel threads, but we also do not want to do too many threads
  81   // that will overwhelm the OS scheduler. Using 1/2 of available threads seems to be a fair
  82   // compromise here. Due to implementation constraints, it should not be lower than
  83   // the number of concurrent threads.
  84   bool ergo_parallel = FLAG_IS_DEFAULT(ParallelGCThreads);
  85   if (ergo_parallel) {
  86     FLAG_SET_DEFAULT(ParallelGCThreads, MAX2(1, os::initial_active_processor_count() / 2));
  87   }
  88 
  89   if (ParallelGCThreads == 0) {
  90     vm_exit_during_initialization("Shenandoah expects ParallelGCThreads > 0, check -XX:ParallelGCThreads=#");
  91   }
  92 
  93   // Make sure ergonomic decisions do not break the thread count invariants.
  94   // This may happen when user overrides one of the flags, but not the other.
  95   // When that happens, we want to adjust the setting that was set ergonomically.
  96   if (ParallelGCThreads < ConcGCThreads) {
  97     if (ergo_conc && !ergo_parallel) {
  98       FLAG_SET_DEFAULT(ConcGCThreads, ParallelGCThreads);
  99     } else if (!ergo_conc && ergo_parallel) {
 100       FLAG_SET_DEFAULT(ParallelGCThreads, ConcGCThreads);
 101     } else if (ergo_conc && ergo_parallel) {
 102       // Should not happen, check the ergonomic computation above. Fail with relevant error.
 103       vm_exit_during_initialization("Shenandoah thread count ergonomic error");
 104     } else {
 105       // User settings error, report and ask user to rectify.
 106       vm_exit_during_initialization("Shenandoah expects ConcGCThreads <= ParallelGCThreads, check -XX:ParallelGCThreads, -XX:ConcGCThreads");
 107     }
 108   }
 109 
 110   if (FLAG_IS_DEFAULT(ParallelRefProcEnabled)) {
 111     FLAG_SET_DEFAULT(ParallelRefProcEnabled, true);
 112   }
 113 
 114   if (ShenandoahRegionSampling && FLAG_IS_DEFAULT(PerfDataMemorySize)) {
 115     // When sampling is enabled, max out the PerfData memory to get more
 116     // Shenandoah data in, including Matrix.
 117     FLAG_SET_DEFAULT(PerfDataMemorySize, 2048*K);
 118   }
 119 
 120 #ifdef COMPILER2
 121   // Shenandoah cares more about pause times, rather than raw throughput.
 122   if (FLAG_IS_DEFAULT(UseCountedLoopSafepoints)) {
 123     FLAG_SET_DEFAULT(UseCountedLoopSafepoints, true);
 124     if (FLAG_IS_DEFAULT(LoopStripMiningIter)) {
 125       FLAG_SET_DEFAULT(LoopStripMiningIter, 1000);
 126     }
 127   }
 128 #ifdef ASSERT
 129   // C2 barrier verification is only reliable when all default barriers are enabled
 130   if (ShenandoahVerifyOptoBarriers &&
 131           (!FLAG_IS_DEFAULT(ShenandoahSATBBarrier)            ||
 132            !FLAG_IS_DEFAULT(ShenandoahLoadRefBarrier)         ||
 133            !FLAG_IS_DEFAULT(ShenandoahStoreValEnqueueBarrier) ||
 134            !FLAG_IS_DEFAULT(ShenandoahCASBarrier)             ||
 135            !FLAG_IS_DEFAULT(ShenandoahCloneBarrier)
 136           )) {
 137     warning("Unusual barrier configuration, disabling C2 barrier verification");
 138     FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
 139   }
 140 #else
 141   guarantee(!ShenandoahVerifyOptoBarriers, "Should be disabled");
 142 #endif // ASSERT
 143 #endif // COMPILER2
 144 
 145   if (AlwaysPreTouch) {
 146     // Shenandoah handles pre-touch on its own. It does not let the
 147     // generic storage code to do the pre-touch before Shenandoah has
 148     // a chance to do it on its own.
 149     FLAG_SET_DEFAULT(AlwaysPreTouch, false);
 150     FLAG_SET_DEFAULT(ShenandoahAlwaysPreTouch, true);
 151   }
 152 
 153   // Shenandoah C2 optimizations apparently dislike the shape of thread-local handshakes.
 154   // Disable it by default, unless we enable it specifically for debugging.
 155   if (FLAG_IS_DEFAULT(ThreadLocalHandshakes)) {
 156     if (ThreadLocalHandshakes) {
 157       FLAG_SET_DEFAULT(ThreadLocalHandshakes, false);
 158     }
 159   } else {
 160     if (ThreadLocalHandshakes) {
 161       warning("Thread-local handshakes are not working correctly with Shenandoah at the moment. Enable at your own risk.");
 162     }
 163   }
 164 
 165   // Record more information about previous cycles for improved debugging pleasure
 166   if (FLAG_IS_DEFAULT(LogEventsBufferEntries)) {
 167     FLAG_SET_DEFAULT(LogEventsBufferEntries, 250);
 168   }
 169 
 170   if (ShenandoahAlwaysPreTouch) {
 171     if (!FLAG_IS_DEFAULT(ShenandoahUncommit)) {
 172       warning("AlwaysPreTouch is enabled, disabling ShenandoahUncommit");
 173     }
 174     FLAG_SET_DEFAULT(ShenandoahUncommit, false);
 175   }
 176 
 177   if ((InitialHeapSize == MaxHeapSize) && ShenandoahUncommit) {
 178     log_info(gc)("Min heap equals to max heap, disabling ShenandoahUncommit");
 179     FLAG_SET_DEFAULT(ShenandoahUncommit, false);
 180   }
 181 
 182   // If class unloading is disabled, no unloading for concurrent cycles as well.
 183   // If class unloading is enabled, users should opt-in for unloading during
 184   // concurrent cycles.
 185   if (!ClassUnloading || !FLAG_IS_CMDLINE(ClassUnloadingWithConcurrentMark)) {
 186     log_info(gc)("Consider -XX:+ClassUnloadingWithConcurrentMark if large pause times "
 187                  "are observed on class-unloading sensitive workloads");
 188     FLAG_SET_DEFAULT(ClassUnloadingWithConcurrentMark, false);
 189   }
 190 
 191   // AOT is not supported yet
 192   if (UseAOT) {
 193     if (!FLAG_IS_DEFAULT(UseAOT)) {
 194       warning("Shenandoah does not support AOT at this moment, disabling UseAOT");
 195     }
 196     FLAG_SET_DEFAULT(UseAOT, false);
 197   }
 198 
 199   // TLAB sizing policy makes resizing decisions before each GC cycle. It averages
 200   // historical data, assigning more recent data the weight according to TLABAllocationWeight.
 201   // Current default is good for generational collectors that run frequent young GCs.
 202   // With Shenandoah, GC cycles are much less frequent, so we need we need sizing policy
 203   // to converge faster over smaller number of resizing decisions.
 204   if (FLAG_IS_DEFAULT(TLABAllocationWeight)) {
 205     FLAG_SET_DEFAULT(TLABAllocationWeight, 90);
 206   }
 207 }
 208 
 209 size_t ShenandoahArguments::conservative_max_heap_alignment() {
 210   size_t align = ShenandoahMaxRegionSize;
 211   if (UseLargePages) {
 212     align = MAX2(align, os::large_page_size());
 213   }
 214   return align;
 215 }
 216 
 217 CollectedHeap* ShenandoahArguments::create_heap() {
 218   return create_heap_with_policy<ShenandoahHeap, ShenandoahCollectorPolicy>();
 219 }