[TF port] Add port::GetCurrentCPU and port::NumTotalCPUs.

GetCurrentCPU: returns the current CPU of the calling thread.
NumTotalCPUs: attempts to get the total number of physical cores on the system

When both return non-failing values, we expect 0 <= GetCurrentCPU < NumTotalCPUs.

PiperOrigin-RevId: 225088316

tensorflow/core/platform/cpu_info.h

@@ -32,9 +32,22 @@ namespace port {
 // Returns an estimate of the number of schedulable CPUs for this
 // process.  Usually, it's constant throughout the lifetime of a
 // process, but it might change if the underlying cluster management
-// software can change it dynamically.
+// software can change it dynamically.  If the underlying call fails, a default
+// value (e.g. `4`) may be returned.
 int NumSchedulableCPUs();
 
+// Returns the total number of CPUs on the system.  This number should
+// not change even if the underlying cluster management software may
+// change the number of schedulable CPUs.  Unlike `NumSchedulableCPUs`, if the
+// underlying call fails, an invalid value of -1 will be returned;
+// the user must check for validity.
+static constexpr int kUnknownCPU = -1;
+int NumTotalCPUs();
+
+// Returns the id of the current CPU.  Returns -1 if the current CPU cannot be
+// identified.  If successful, the return value will be in [0, NumTotalCPUs()).
+int GetCurrentCPU();
+
 // Returns an estimate of the number of hyperthreads per physical core
 // on the CPU
 int NumHyperthreadsPerCore();

tensorflow/core/platform/port_test.cc

@@ -33,6 +33,12 @@ TEST(Port, AlignedMalloc) {
   }
 }
 
+TEST(Port, GetCurrentCPU) {
+  const int cpu = GetCurrentCPU();
+  EXPECT_GE(cpu, 0);
+  EXPECT_LT(cpu, NumTotalCPUs());
+}
+
 TEST(ConditionVariable, WaitForMilliseconds_Timeout) {
   mutex m;
   mutex_lock l(m);
@@ -78,3 +84,9 @@ TEST(TestCPUFeature, TestFeature) {
 
 }  // namespace port
 }  // namespace tensorflow
+
+int main(int argc, char** argv) {
+  // On Linux, add: FLAGS_logtostderr = true;
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

tensorflow/core/platform/posix/port.cc

@@ -25,7 +25,14 @@ limitations under the License.
 #if defined(__linux__) && !defined(__ANDROID__)
 #include <sched.h>
 #include <sys/sysinfo.h>
+#else
+#include <sys/syscall.h>
+#endif
+
+#if !defined(__APPLE__) && (__x86_64__ || __i386__)
+#include <cpuid.h>
 #endif
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -69,6 +76,34 @@ int NumSchedulableCPUs() {
   return kDefaultCores;
 }
 
+int NumTotalCPUs() {
+  int count = absl::base_internal::NumCPUs();
+  return (count == 0) ? kUnknownCPU : count;
+}
+
+int GetCurrentCPU() {
+#if defined(__linux__) && !defined(__ANDROID__)
+  return sched_getcpu();
+#elif defined(__cpuid_count)
+  // Attempt to use cpuid on all other platforms.  If that fails, perform a
+  // syscall.
+  uint32_t eax, ebx, ecx, edx;
+  __cpuid_count(/*leaf=*/1, /*subleaf=*/0, eax, ebx, ecx, edx);
+  if ((edx & (1 << 9)) != 0) {
+    // EBX bits 24-31 are APIC ID
+    return static_cast<unsigned int>(ebx >> 24);
+  }
+#elif defined(__NR_getcpu)
+  unsigned int cpu;
+  if (syscall(__NR_getcpu, &cpu, NULL, NULL) < 0) {
+    return kUnknownCPU;
+  } else {
+    return static_cast<int>(cpu);
+  }
+#endif
+  return kUnknownCPU;
+}
+
 int NumHyperthreadsPerCore() {
   static const int ht_per_core = tensorflow::port::CPUIDNumSMT();
   return (ht_per_core > 0) ? ht_per_core : 1;
@@ -83,9 +118,7 @@ int NUMANumNodes() { return 1; }
 
 void NUMASetThreadNodeAffinity(int node) {}
 
-int NUMAGetThreadNodeAffinity() {
-  return kNUMANoAffinity;
-}
+int NUMAGetThreadNodeAffinity() { return kNUMANoAffinity; }
 
 void* AlignedMalloc(size_t size, int minimum_alignment) {
 #if defined(__ANDROID__)

tensorflow/core/platform/windows/port.cc

@@ -21,6 +21,7 @@ limitations under the License.
 #endif
 
 #include <Windows.h>
+#include <processthreadsapi.h>
 #include <shlwapi.h>
 
 #include "tensorflow/core/platform/cpu_info.h"
@@ -54,6 +55,30 @@ int NumSchedulableCPUs() {
   return system_info.dwNumberOfProcessors;
 }
 
+int NumTotalCPUs() {
+  // TODO(ebrevdo): Make this more accurate.
+  //
+  // This only returns the number of processors in the current
+  // processor group; which may be undercounting if you have more than 64 cores.
+  // For that case, one needs to call
+  // GetLogicalProcessorInformationEx(RelationProcessorCore, ...) and accumulate
+  // the Size fields by iterating over the written-to buffer.  Since I can't
+  // easily test this on Windows, I'm deferring this to someone who can!
+  //
+  // If you fix this, also consider updatig GetCurrentCPU below.
+  return NumSchedulableCPUs();
+}
+
+int GetCurrentCPU() {
+  // NOTE(ebrevdo): This returns the processor number within the processor
+  // group on systems with >64 processors.  Therefore it doesn't necessarily map
+  // naturally to an index in NumSchedulableCPUs().
+  //
+  // On the plus side, this number is probably guaranteed to be within
+  // [0, NumTotalCPUs()) due to its incomplete implementation.
+  return GetCurrentProcessorNumber();
+}
+
 bool NUMAEnabled() {
   // Not yet implemented: coming soon.
   return false;