1 /*
2 * Copyright (c) 2019, 2020, Oracle and/or its affiliates. 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 #include "precompiled.hpp"
25 #include "gc/z/zCPU.inline.hpp"
26 #include "gc/z/zGlobals.hpp"
27 #include "gc/z/zHeuristics.hpp"
28 #include "logging/log.hpp"
29 #include "runtime/globals.hpp"
30 #include "runtime/os.hpp"
31 #include "utilities/globalDefinitions.hpp"
32 #include "utilities/powerOfTwo.hpp"
33
34 void ZHeuristics::set_medium_page_size() {
35 // Set ZPageSizeMedium so that a medium page occupies at most 3.125% of the
36 // max heap size. ZPageSizeMedium is initially set to 0, which means medium
37 // pages are effectively disabled. It is adjusted only if ZPageSizeMedium
38 // becomes larger than ZPageSizeSmall.
39 const size_t min = ZGranuleSize;
40 const size_t max = ZGranuleSize * 16;
41 const size_t unclamped = MaxHeapSize * 0.03125;
42 const size_t clamped = clamp(unclamped, min, max);
43 const size_t size = round_down_power_of_2(clamped);
44
45 if (size > ZPageSizeSmall) {
46 // Enable medium pages
47 ZPageSizeMedium = size;
48 ZPageSizeMediumShift = log2_intptr(ZPageSizeMedium);
49 ZObjectSizeLimitMedium = ZPageSizeMedium / 8;
50 ZObjectAlignmentMediumShift = (int)ZPageSizeMediumShift - 13;
51 ZObjectAlignmentMedium = 1 << ZObjectAlignmentMediumShift;
52 }
53 }
54
55 size_t ZHeuristics::max_reserve() {
56 // Reserve one small page per worker plus one shared medium page. This is still just
57 // an estimate and doesn't guarantee that we can't run out of memory during relocation.
58 const uint nworkers = MAX2(ParallelGCThreads, ConcGCThreads);
59 const size_t reserve = (nworkers * ZPageSizeSmall) + ZPageSizeMedium;
60 return MIN2(MaxHeapSize, reserve);
61 }
62
63 bool ZHeuristics::use_per_cpu_shared_small_pages() {
64 // Use per-CPU shared small pages only if these pages occupy at most 3.125%
65 // of the max heap size. Otherwise fall back to using a single shared small
66 // page. This is useful when using small heaps on large machines.
67 const size_t per_cpu_share = (MaxHeapSize * 0.03125) / ZCPU::count();
68 return per_cpu_share >= ZPageSizeSmall;
69 }
70
71 static uint nworkers_based_on_ncpus(double cpu_share_in_percent) {
72 return ceil(os::initial_active_processor_count() * cpu_share_in_percent / 100.0);
73 }
74
75 static uint nworkers_based_on_heap_size(double reserve_share_in_percent) {
76 const int nworkers = (MaxHeapSize * (reserve_share_in_percent / 100.0)) / ZPageSizeSmall;
77 return MAX2(nworkers, 1);
78 }
79
80 static uint nworkers(double cpu_share_in_percent) {
81 // Cap number of workers so that we don't use more than 2% of the max heap
82 // for the small page reserve. This is useful when using small heaps on
83 // large machines.
84 return MIN2(nworkers_based_on_ncpus(cpu_share_in_percent),
85 nworkers_based_on_heap_size(2.0));
86 }
87
88 uint ZHeuristics::nparallel_workers() {
89 // Use 60% of the CPUs, rounded up. We would like to use as many threads as
90 // possible to increase parallelism. However, using a thread count that is
91 // close to the number of processors tends to lead to over-provisioning and
92 // scheduling latency issues. Using 60% of the active processors appears to
93 // be a fairly good balance.
94 return nworkers(60.0);
95 }
96
97 uint ZHeuristics::nconcurrent_workers() {
98 // Use 12.5% of the CPUs, rounded up. The number of concurrent threads we
99 // would like to use heavily depends on the type of workload we are running.
100 // Using too many threads will have a negative impact on the application
101 // throughput, while using too few threads will prolong the GC-cycle and
102 // we then risk being out-run by the application. Using 12.5% of the active
103 // processors appears to be a fairly good balance.
104 return nworkers(12.5);
105 }