[backport] Add support for cgroupv2. (dmlc#9651) (dmlc#9656)

Author: trivialfis

src/common/threading_utils.cc

@@ -3,14 +3,23 @@
  */
 #include "threading_utils.h"
 
-#include <fstream>
-#include <string>
+#include <algorithm>   // for max
+#include <exception>   // for exception
+#include <filesystem>  // for path, exists
+#include <fstream>     // for ifstream
+#include <string>      // for string
 
-#include "xgboost/logging.h"
+#include "common.h"  // for DivRoundUp
 
-namespace xgboost {
-namespace common {
-int32_t GetCfsCPUCount() noexcept {
+namespace xgboost::common {
+/**
+ * Modified from
+ * github.com/psiha/sweater/blob/master/include/boost/sweater/hardware_concurrency.hpp
+ *
+ * MIT License: Copyright (c) 2016 Domagoj Šarić
+ */
+std::int32_t GetCGroupV1Count(std::filesystem::path const& quota_path,
+                              std::filesystem::path const& peroid_path) {
 #if defined(__linux__)
   // https://bugs.openjdk.java.net/browse/JDK-8146115
   // http://hg.openjdk.java.net/jdk/hs/rev/7f22774a5f42
@@ -31,15 +40,56 @@ int32_t GetCfsCPUCount() noexcept {
     }
   };
   // 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"));
+  auto const cfs_quota(read_int(quota_path.c_str()));
+  auto const cfs_period(read_int(peroid_path.c_str()));
   if ((cfs_quota > 0) && (cfs_period > 0)) {
     return std::max(cfs_quota / cfs_period, 1);
   }
 #endif  //  defined(__linux__)
   return -1;
 }
 
+std::int32_t GetCGroupV2Count(std::filesystem::path const& bandwidth_path) noexcept(true) {
+  std::int32_t cnt{-1};
+#if defined(__linux__)
+  namespace fs = std::filesystem;
+
+  std::int32_t a{0}, b{0};
+
+  auto warn = [] { LOG(WARNING) << "Invalid cgroupv2 file."; };
+  try {
+    std::ifstream fin{bandwidth_path, std::ios::in};
+    fin >> a;
+    fin >> b;
+  } catch (std::exception const&) {
+    warn();
+    return cnt;
+  }
+  if (a > 0 && b > 0) {
+    cnt = std::max(common::DivRoundUp(a, b), 1);
+  }
+#endif  //  defined(__linux__)
+  return cnt;
+}
+
+std::int32_t GetCfsCPUCount() noexcept {
+  namespace fs = std::filesystem;
+  fs::path const bandwidth_path{"/sys/fs/cgroup/cpu.max"};
+  auto has_v2 = fs::exists(bandwidth_path);
+  if (has_v2) {
+    return GetCGroupV2Count(bandwidth_path);
+  }
+
+  fs::path const quota_path{"/sys/fs/cgroup/cpu/cpu.cfs_quota_us"};
+  fs::path const peroid_path{"/sys/fs/cgroup/cpu/cpu.cfs_period_us"};
+  auto has_v1 = fs::exists(quota_path) && fs::exists(peroid_path);
+  if (has_v1) {
+    return GetCGroupV1Count(quota_path, peroid_path);
+  }
+
+  return -1;
+}
+
 std::int32_t OmpGetNumThreads(std::int32_t n_threads) {
   // Don't use parallel if we are in a parallel region.
   if (omp_in_parallel()) {
@@ -54,5 +104,4 @@ std::int32_t OmpGetNumThreads(std::int32_t n_threads) {
   n_threads = std::max(n_threads, 1);
   return n_threads;
 }
-}  // namespace common
-}  // namespace xgboost
+}  // namespace xgboost::common

src/common/threading_utils.h

@@ -253,11 +253,6 @@ inline std::int32_t OmpGetThreadLimit() {
  * \brief Get thread limit from CFS.
  *
  *   This function has non-trivial overhead and should not be called repeatly.
- *
- * Modified from
- * github.com/psiha/sweater/blob/master/include/boost/sweater/hardware_concurrency.hpp
- *
- * MIT License: Copyright (c) 2016 Domagoj Šarić
  */
 std::int32_t GetCfsCPUCount() noexcept;