1 //===-- llvm/Support/Threading.cpp- Control multithreading mode --*- C++ -*-==//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines helper functions for running LLVM in a multi-threaded
10 // environment.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/Support/Threading.h"
15 #include "llvm/Config/config.h"
16 #include "llvm/Config/llvm-config.h"
17
18 #include <cassert>
19 #include <errno.h>
20 #include <optional>
21 #include <stdlib.h>
22 #include <string.h>
23
24 using namespace llvm;
25
26 //===----------------------------------------------------------------------===//
27 //=== WARNING: Implementation here must contain only TRULY operating system
28 //=== independent code.
29 //===----------------------------------------------------------------------===//
30
31 #if LLVM_ENABLE_THREADS == 0 || \
32 (!defined(_WIN32) && !defined(HAVE_PTHREAD_H))
get_threadid()33 uint64_t llvm::get_threadid() { return 0; }
34
get_max_thread_name_length()35 uint32_t llvm::get_max_thread_name_length() { return 0; }
36
set_thread_name(const Twine & Name)37 void llvm::set_thread_name(const Twine &Name) {}
38
get_thread_name(SmallVectorImpl<char> & Name)39 void llvm::get_thread_name(SmallVectorImpl<char> &Name) { Name.clear(); }
40
get_thread_affinity_mask()41 llvm::BitVector llvm::get_thread_affinity_mask() { return {}; }
42
compute_thread_count() const43 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
44 // When threads are disabled, ensure clients will loop at least once.
45 return 1;
46 }
47
48 // Unknown if threading turned off
get_physical_cores()49 int llvm::get_physical_cores() { return -1; }
50
51 #else
52
53 static int computeHostNumHardwareThreads();
54
compute_thread_count() const55 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
56 int MaxThreadCount =
57 UseHyperThreads ? computeHostNumHardwareThreads() : get_physical_cores();
58 if (MaxThreadCount <= 0)
59 MaxThreadCount = 1;
60 // Damage control threading.
61 //
62 // There are no heuristics to figure out how many threads makes sense to spawn,
63 // all while rolling with all available hw threads starts being detrimental to
64 // performance really early.
65 //
66 // Work around by putting a hard cap unless the user explicitly requested a certain amount.
67 //
68 // See https://discourse.llvm.org/t/avoidable-overhead-from-threading-by-default/69160
69 // for more details.
70 if (ThreadsRequested == 0) {
71 return std::min(MaxThreadCount, 4);
72 }
73 if (!Limit)
74 return ThreadsRequested;
75 return std::min((unsigned)MaxThreadCount, ThreadsRequested);
76 }
77
78 // Include the platform-specific parts of this class.
79 #ifdef LLVM_ON_UNIX
80 #include "Unix/Threading.inc"
81 #endif
82 #ifdef _WIN32
83 #include "Windows/Threading.inc"
84 #endif
85
86 // Must be included after Threading.inc to provide definition for llvm::thread
87 // because FreeBSD's condvar.h (included by user.h) misuses the "thread"
88 // keyword.
89 #include "llvm/Support/thread.h"
90
91 #if defined(__APPLE__)
92 // Darwin's default stack size for threads except the main one is only 512KB,
93 // which is not enough for some/many normal LLVM compilations. This implements
94 // the same interface as std::thread but requests the same stack size as the
95 // main thread (8MB) before creation.
96 const std::optional<unsigned> llvm::thread::DefaultStackSize = 8 * 1024 * 1024;
97 #elif defined(_AIX)
98 // On AIX, the default pthread stack size limit is ~192k for 64-bit programs.
99 // This limit is easily reached when doing link-time thinLTO. AIX library
100 // developers have used 4MB, so we'll do the same.
101 const std::optional<unsigned> llvm::thread::DefaultStackSize = 4 * 1024 * 1024;
102 #else
103 const std::optional<unsigned> llvm::thread::DefaultStackSize;
104 #endif
105
106
107 #endif
108
109 std::optional<ThreadPoolStrategy>
get_threadpool_strategy(StringRef Num,ThreadPoolStrategy Default)110 llvm::get_threadpool_strategy(StringRef Num, ThreadPoolStrategy Default) {
111 if (Num == "all")
112 return llvm::hardware_concurrency();
113 if (Num.empty())
114 return Default;
115 unsigned V;
116 if (Num.getAsInteger(10, V))
117 return std::nullopt; // malformed 'Num' value
118 if (V == 0)
119 return Default;
120
121 // Do not take the Default into account. This effectively disables
122 // heavyweight_hardware_concurrency() if the user asks for any number of
123 // threads on the cmd-line.
124 ThreadPoolStrategy S = llvm::hardware_concurrency();
125 S.ThreadsRequested = V;
126 return S;
127 }
128