[Support] Move getHostNumPhysicalCores to Threading.h

This change is focussed on simplifying `Support/Host.h` to only do
target detection. In this case, this function is close in usage to
existing functions in `Support/Threading.h`, so I moved it into there.
The function is also renamed to `llvm::get_physical_cores()` to match
the style of threading's functions.

Differential Revision: https://reviews.llvm.org/D137836

1 files changed, 129 insertions, 3 deletions

diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index bd954fd..6c2ff11 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -13,8 +13,12 @@
 
 #include "llvm/Support/Threading.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Config/config.h"
-#include "llvm/Support/Host.h"
+#include "llvm/Config/llvm-config.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/raw_ostream.h"
 
 #include <cassert>
 #include <errno.h>
@@ -50,8 +54,8 @@ unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
 static int computeHostNumHardwareThreads();
 
 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
-  int MaxThreadCount = UseHyperThreads ? computeHostNumHardwareThreads()
-                                       : sys::getHostNumPhysicalCores();
+  int MaxThreadCount =
+      UseHyperThreads ? computeHostNumHardwareThreads() : get_physical_cores();
   if (MaxThreadCount <= 0)
     MaxThreadCount = 1;
   if (ThreadsRequested == 0)
@@ -106,3 +110,125 @@ llvm::get_threadpool_strategy(StringRef Num, ThreadPoolStrategy Default) {
   S.ThreadsRequested = V;
   return S;
 }
+
+#if defined(__linux__) && (defined(__i386__) || defined(__x86_64__))
+// On Linux, the number of physical cores can be computed from /proc/cpuinfo,
+// using the number of unique physical/core id pairs. The following
+// implementation reads the /proc/cpuinfo format on an x86_64 system.
+static int computeHostNumPhysicalCores() {
+  // Enabled represents the number of physical id/core id pairs with at least
+  // one processor id enabled by the CPU affinity mask.
+  cpu_set_t Affinity, Enabled;
+  if (sched_getaffinity(0, sizeof(Affinity), &Affinity) != 0)
+    return -1;
+  CPU_ZERO(&Enabled);
+
+  // Read /proc/cpuinfo as a stream (until EOF reached). It cannot be
+  // mmapped because it appears to have 0 size.
+  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Text =
+      llvm::MemoryBuffer::getFileAsStream("/proc/cpuinfo");
+  if (std::error_code EC = Text.getError()) {
+    llvm::errs() << "Can't read "
+                 << "/proc/cpuinfo: " << EC.message() << "\n";
+    return -1;
+  }
+  SmallVector<StringRef, 8> strs;
+  (*Text)->getBuffer().split(strs, "\n", /*MaxSplit=*/-1,
+                             /*KeepEmpty=*/false);
+  int CurProcessor = -1;
+  int CurPhysicalId = -1;
+  int CurSiblings = -1;
+  int CurCoreId = -1;
+  for (StringRef Line : strs) {
+    std::pair<StringRef, StringRef> Data = Line.split(':');
+    auto Name = Data.first.trim();
+    auto Val = Data.second.trim();
+    // These fields are available if the kernel is configured with CONFIG_SMP.
+    if (Name == "processor")
+      Val.getAsInteger(10, CurProcessor);
+    else if (Name == "physical id")
+      Val.getAsInteger(10, CurPhysicalId);
+    else if (Name == "siblings")
+      Val.getAsInteger(10, CurSiblings);
+    else if (Name == "core id") {
+      Val.getAsInteger(10, CurCoreId);
+      // The processor id corresponds to an index into cpu_set_t.
+      if (CPU_ISSET(CurProcessor, &Affinity))
+        CPU_SET(CurPhysicalId * CurSiblings + CurCoreId, &Enabled);
+    }
+  }
+  return CPU_COUNT(&Enabled);
+}
+#elif defined(__linux__) && defined(__s390x__)
+static int computeHostNumPhysicalCores() {
+  return sysconf(_SC_NPROCESSORS_ONLN);
+}
+#elif defined(__linux__) && !defined(__ANDROID__)
+static int computeHostNumPhysicalCores() {
+  cpu_set_t Affinity;
+  if (sched_getaffinity(0, sizeof(Affinity), &Affinity) == 0)
+    return CPU_COUNT(&Affinity);
+
+  // The call to sched_getaffinity() may have failed because the Affinity
+  // mask is too small for the number of CPU's on the system (i.e. the
+  // system has more than 1024 CPUs). Allocate a mask large enough for
+  // twice as many CPUs.
+  cpu_set_t *DynAffinity;
+  DynAffinity = CPU_ALLOC(2048);
+  if (sched_getaffinity(0, CPU_ALLOC_SIZE(2048), DynAffinity) == 0) {
+    int NumCPUs = CPU_COUNT(DynAffinity);
+    CPU_FREE(DynAffinity);
+    return NumCPUs;
+  }
+  return -1;
+}
+#elif defined(__APPLE__)
+// Gets the number of *physical cores* on the machine.
+static int computeHostNumPhysicalCores() {
+  uint32_t count;
+  size_t len = sizeof(count);
+  sysctlbyname("hw.physicalcpu", &count, &len, NULL, 0);
+  if (count < 1) {
+    int nm[2];
+    nm[0] = CTL_HW;
+    nm[1] = HW_AVAILCPU;
+    sysctl(nm, 2, &count, &len, NULL, 0);
+    if (count < 1)
+      return -1;
+  }
+  return count;
+}
+#elif defined(__MVS__)
+static int computeHostNumPhysicalCores() {
+  enum {
+    // Byte offset of the pointer to the Communications Vector Table (CVT) in
+    // the Prefixed Save Area (PSA). The table entry is a 31-bit pointer and
+    // will be zero-extended to uintptr_t.
+    FLCCVT = 16,
+    // Byte offset of the pointer to the Common System Data Area (CSD) in the
+    // CVT. The table entry is a 31-bit pointer and will be zero-extended to
+    // uintptr_t.
+    CVTCSD = 660,
+    // Byte offset to the number of live CPs in the LPAR, stored as a signed
+    // 32-bit value in the table.
+    CSD_NUMBER_ONLINE_STANDARD_CPS = 264,
+  };
+  char *PSA = 0;
+  char *CVT = reinterpret_cast<char *>(
+      static_cast<uintptr_t>(reinterpret_cast<unsigned int &>(PSA[FLCCVT])));
+  char *CSD = reinterpret_cast<char *>(
+      static_cast<uintptr_t>(reinterpret_cast<unsigned int &>(CVT[CVTCSD])));
+  return reinterpret_cast<int &>(CSD[CSD_NUMBER_ONLINE_STANDARD_CPS]);
+}
+#elif defined(_WIN32) && LLVM_ENABLE_THREADS != 0
+// Defined in llvm/lib/Support/Windows/Threading.inc
+int computeHostNumPhysicalCores();
+#else
+// On other systems, return -1 to indicate unknown.
+static int computeHostNumPhysicalCores() { return -1; }
+#endif
+
+int llvm::get_physical_cores() {
+  static int NumCores = computeHostNumPhysicalCores();
+  return NumCores;
+}