Honor CPU counts from CFS. (#7654)

src/common/threading_utils.cc

@@ -0,0 +1,51 @@
+/*!
+ * Copyright 2022 by XGBoost Contributors
+ */
+#include "threading_utils.h"
+#if defined(__linux__)
+#include <fcntl.h>
+#include <unistd.h>
+#endif  // defined(__linux__)
+#include "xgboost/logging.h"
+
+namespace xgboost {
+namespace common {
+/**
+ * \brief Get thread limit from CFS
+ *
+ * Modified from
+ * github.com/psiha/sweater/blob/master/include/boost/sweater/hardware_concurrency.hpp
+ *
+ * MIT License: Copyright (c) 2016 Domagoj Šarić
+ */
+int32_t GetCfsCPUCount() noexcept {
+#if defined(__linux__)
+  // https://bugs.openjdk.java.net/browse/JDK-8146115
+  // http://hg.openjdk.java.net/jdk/hs/rev/7f22774a5f42
+  // RAM limit /sys/fs/cgroup/memory.limit_in_bytes
+  // swap limt /sys/fs/cgroup/memory.memsw.limit_in_bytes
+
+  auto read_int = [](char const* const file_path) noexcept {
+    auto const fd(::open(file_path, O_RDONLY, 0));
+    if (fd == -1) {
+      return -1;
+    }
+    char value[64];
+    CHECK(::read(fd, value, sizeof(value)) < signed(sizeof(value)));
+    try {
+      return std::stoi(value);
+    } catch (std::exception const&) {
+      return -1;
+    }
+  };
+  // complete fair scheduler from Linux
+  auto const cfs_quota(read_int("/sys/fs/cgroup/cpu/cpu.cfs_quota_us"));
+  auto const cfs_period(read_int("/sys/fs/cgroup/cpu/cpu.cfs_period_us"));
+  if ((cfs_quota > 0) && (cfs_period > 0)) {
+    return std::max(cfs_quota / cfs_period, 1);
+  }
+#endif  //  defined(__linux__)
+  return -1;
+}
+}  // namespace common
+}  // namespace xgboost

src/common/threading_utils.h

@@ -1,7 +1,5 @@
 /*!
- * Copyright 2015-2019 by Contributors
- * \file common.h
- * \brief Threading utilities
+ * Copyright 2019-2022 by XGBoost Contributors
  */
 #ifndef XGBOOST_COMMON_THREADING_UTILS_H_
 #define XGBOOST_COMMON_THREADING_UTILS_H_
@@ -238,6 +236,8 @@ inline int32_t OmpGetThreadLimit() {
   return limit;
 }
 
+int32_t GetCfsCPUCount() noexcept;
+
 inline int32_t OmpGetNumThreads(int32_t n_threads) {
   if (n_threads <= 0) {
     n_threads = std::min(omp_get_num_procs(), omp_get_max_threads());