Added method to set thread affinity for a certain core

CMakeLists.txt

@@ -48,6 +48,9 @@ if(BUILD_TESTING)
   find_package(rclcpp_lifecycle REQUIRED)
   find_package(test_msgs REQUIRED)
 
+  ament_add_gmock(thread_priority_tests test/thread_priority_tests.cpp)
+  target_link_libraries(thread_priority_tests thread_priority)
+
   ament_add_gmock(realtime_box_tests test/realtime_box_tests.cpp)
   target_link_libraries(realtime_box_tests realtime_tools)
 

include/realtime_tools/thread_priority.hpp

@@ -46,6 +46,18 @@ bool has_realtime_kernel();
  */
 bool configure_sched_fifo(int priority);
 
+/**
+ * Configure the caller thread affinity - Tell the scheduler to prefer a certain core for the current thread
+ * \param[in] core - the number of the core
+ * \returns true if configuring the scheduler succeeded
+*/
+bool set_preferred_core(const int core = -1);
+
+/**
+ * \returns The amount of available cpu cores
+*/
+int get_core_count();
+
 /**
  * Locks the memory pages of the calling thread to prevent page faults. By calling this method, the programs locks all pages mapped into the address space of the calling process and future mappings. This means that the kernel will not swap out the pages to disk i.e., the pages are guaranteed to stay in RAM until later unlocked - which is important for realtime applications.
  * \param[out] message a message describing the result of the operation

src/thread_priority.cpp

@@ -36,8 +36,10 @@
 #include <sys/mman.h>
 #endif
 
+#include <unistd.h>
 #include <cstring>
 #include <fstream>
+#include <iostream>
 
 namespace realtime_tools
 {
@@ -64,6 +66,58 @@ bool configure_sched_fifo(int priority)
 #endif
 }
 
+static void print_error(const int errc)
+{
+  switch (errc) {
+    case 0:
+      return;
+    case EFAULT:
+      std::cerr << "Call of sched_setaffinity with invalid cpuset" << std::endl;
+      return;
+    case EINVAL:
+      std::cerr << "Call of sched_setaffinity with an invalid cpu core" << std::endl;
+      return;
+    case ESRCH:
+      std::cerr << "Call of sched_setaffinity with and invalid thread id/process id" << std::endl;
+      return;
+    default:
+      std::cerr << "Error code: " << errc << ": " << std::string(strerror(errc)) << std::endl;
+  }
+}
+
+bool set_preferred_core(const int core)
+{
+  // Allow attaching the thread/process to a certain cpu core
+  cpu_set_t cpuset;
+  CPU_ZERO(&cpuset);
+  // Obtain amount of cores/
+  const auto number_of_cores = get_core_count();
+
+  // Reset affinity by setting it to all cores
+  if (core < 0) {
+    for (int i{0}; i < number_of_cores; i++) {
+      CPU_SET(i, &cpuset);
+    }
+    // And actually tell the schedular to set the affinity of the currently calling thread
+    const auto result = sched_setaffinity(0, sizeof(cpu_set_t), &cpuset);
+    print_error(result);
+    return result == 0;
+  }
+
+  if (core < number_of_cores) {
+    // Set the passed core to the cpu set
+    CPU_SET(core, &cpuset);
+    // And actually tell the schedular to set the affinity of the currently calling thread
+    const auto result = sched_setaffinity(0, sizeof(cpu_set_t), &cpuset);
+    print_error(result);
+    return result == 0;
+  }
+  // Invalid core number passed
+  return false;
+}
+
+int get_core_count() { return sysconf(_SC_NPROCESSORS_ONLN); }
+
 bool lock_memory(std::string & message)
 {
 #ifdef _WIN32

test/thread_priority_tests.cpp

@@ -0,0 +1,60 @@
+// Copyright (c) 2024, Lennart Nachtigall
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//    * Redistributions of source code must retain the above copyright
+//      notice, this list of conditions and the following disclaimer.
+//
+//    * Redistributions in binary form must reproduce the above copyright
+//      notice, this list of conditions and the following disclaimer in the
+//      documentation and/or other materials provided with the distribution.
+//
+//    * Neither the name of the Willow Garage, Inc. nor the names of its
+//      contributors may be used to endorse or promote products derived from
+//      this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+
+// Author: Lennart Nachtigall
+
+#include <gmock/gmock.h>
+#include <thread>
+
+#include <realtime_tools/thread_priority.hpp>
+
+TEST(thread_priority, get_core_count)
+{
+  const auto count = realtime_tools::get_core_count();
+
+  EXPECT_EQ(count, std::thread::hardware_concurrency());
+}
+
+TEST(thread_priority, set_preferred_core_valid)
+{
+  // We should always have at least one core
+  EXPECT_TRUE(realtime_tools::set_preferred_core(0));
+}
+
+TEST(thread_priority, set_preferred_core_invalid_too_many_cores)
+{
+  const auto count = realtime_tools::get_core_count();
+  // We should always have at least one core
+  EXPECT_FALSE(realtime_tools::set_preferred_core(count + 10));
+}
+
+TEST(thread_priority, set_preferred_core_valid_reset)
+{
+  // Reset core affinity
+  EXPECT_TRUE(realtime_tools::set_preferred_core(-1));
+}