ctest: Optionally avoid starting tests that may exceed a given CPU load

Add a TestLoad setting to CTest that can be set via a new --test-load
command-line option, CTEST_TEST_LOAD variable, or TEST_LOAD option to
the ctest_test command.  Teach cmCTestMultiProcessHandler to measure
the CPU load and avoid starting tests that may take more than the
spare load currently available.  The expression

 <current_load> + <test_processors> <= <max-load>

must be true to start a new test.

Co-Author: Zack Galbreath <zack.galbreath@kitware.com>

40 files changed, 392 insertions, 7 deletions

diff --git a/Help/command/ctest_memcheck.rst b/Help/command/ctest_memcheck.rst
index 2800511..29bdf7d 100644
--- a/Help/command/ctest_memcheck.rst
+++ b/Help/command/ctest_memcheck.rst
@@ -14,6 +14,7 @@ Perform the :ref:`CTest MemCheck Step` as a :ref:`Dashboard Client`.
                  [EXCLUDE_LABEL <label-exclude-regex>]
                  [INCLUDE_LABEL <label-include-regex>]
                  [PARALLEL_LEVEL <level>]
+                 [TEST_LOAD <threshold>]
                  [SCHEDULE_RANDOM <ON|OFF>]
                  [STOP_TIME <time-of-day>]
                  [RETURN_VALUE <result-var>]
diff --git a/Help/command/ctest_test.rst b/Help/command/ctest_test.rst
index af422b6..162db69 100644
--- a/Help/command/ctest_test.rst
+++ b/Help/command/ctest_test.rst
@@ -14,6 +14,7 @@ Perform the :ref:`CTest Test Step` as a :ref:`Dashboard Client`.
              [EXCLUDE_LABEL <label-exclude-regex>]
              [INCLUDE_LABEL <label-include-regex>]
              [PARALLEL_LEVEL <level>]
+             [TEST_LOAD <threshold>]
              [SCHEDULE_RANDOM <ON|OFF>]
              [STOP_TIME <time-of-day>]
              [RETURN_VALUE <result-var>]
@@ -61,6 +62,13 @@ The options are:
   Specify a positive number representing the number of tests to
   be run in parallel.
 
+``TEST_LOAD <threshold>``
+  While running tests in parallel, try not to start tests when they
+  may cause the CPU load to pass above a given threshold.  If not
+  specified the :variable:`CTEST_TEST_LOAD` variable will be checked,
+  and then the ``--test-load`` command-line argument to :manual:`ctest(1)`.
+  See also the ``TestLoad`` setting in the :ref:`CTest Test Step`.
+
 ``SCHEDULE_RANDOM <ON|OFF>``
   Launch tests in a random order.  This may be useful for detecting
   implicit test dependencies.
diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index 0e6222f..adbc40b 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -386,6 +386,7 @@ Variables for CTest
    /variable/CTEST_SVN_COMMAND
    /variable/CTEST_SVN_OPTIONS
    /variable/CTEST_SVN_UPDATE_OPTIONS
+   /variable/CTEST_TEST_LOAD
    /variable/CTEST_TEST_TIMEOUT
    /variable/CTEST_TRIGGER_SITE
    /variable/CTEST_UPDATE_COMMAND
diff --git a/Help/manual/ctest.1.rst b/Help/manual/ctest.1.rst
index c91321b..50c856a 100644
--- a/Help/manual/ctest.1.rst
+++ b/Help/manual/ctest.1.rst
@@ -66,6 +66,13 @@ Options
  number of jobs.  This option can also be set by setting the
  environment variable ``CTEST_PARALLEL_LEVEL``.
 
+``--test-load <level>``
+ While running tests in parallel (e.g. with ``-j``), try not to start
+ tests when they may cause the CPU load to pass above a given threshold.
+
+ When ``ctest`` is run as a `Dashboard Client`_ this sets the
+ ``TestLoad`` option of the `CTest Test Step`_.
+
 ``-Q,--quiet``
  Make ctest quiet.
 
@@ -776,6 +783,13 @@ Arguments to the command may specify some of the step settings.
 
 Configuration settings include:
 
+``TestLoad``
+  While running tests in parallel (e.g. with ``-j``), try not to start
+  tests when they may cause the CPU load to pass above a given threshold.
+
+  * `CTest Script`_ variable: :variable:`CTEST_TEST_LOAD`
+  * :module:`CTest` module variable: ``CTEST_TEST_LOAD``
+
 ``TimeOut``
   The default timeout for each test if not specified by the
   :prop_test:`TIMEOUT` test property.
diff --git a/Help/release/dev/ctest-test-load-option.rst b/Help/release/dev/ctest-test-load-option.rst
new file mode 100644
index 0000000..069f49a
--- /dev/null
+++ b/Help/release/dev/ctest-test-load-option.rst
@@ -0,0 +1,9 @@
+ctest-test-load-option
+----------------------
+
+* CTest learned to optionally measure the CPU load during parallel
+  testing and avoid starting tests that may cause the load to exceed
+  a given threshold.  See the :manual:`ctest(1)` command ``--test-load``
+  option, the ``TestLoad`` setting of the :ref:`CTest Test Step`,
+  the :variable:`CTEST_TEST_LOAD` variable, and the ``TEST_LOAD``
+  option of the :command:`ctest_test` command.
diff --git a/Help/variable/CTEST_TEST_LOAD.rst b/Help/variable/CTEST_TEST_LOAD.rst
new file mode 100644
index 0000000..80823fe
--- /dev/null
+++ b/Help/variable/CTEST_TEST_LOAD.rst
@@ -0,0 +1,7 @@
+CTEST_TEST_LOAD
+---------------
+
+Specify the ``TestLoad`` setting in the :ref:`CTest Test Step`
+of a :manual:`ctest(1)` dashboard client script.  This sets the
+default value for the ``TEST_LOAD`` option of the :command:`ctest_test`
+command.
diff --git a/Modules/DartConfiguration.tcl.in b/Modules/DartConfiguration.tcl.in
index 37a0a40..918b407 100644
--- a/Modules/DartConfiguration.tcl.in
+++ b/Modules/DartConfiguration.tcl.in
@@ -95,6 +95,10 @@ SlurmRunCommand: @SLURM_SRUN_COMMAND@
 # Currently set to 25 minutes
 TimeOut: @DART_TESTING_TIMEOUT@
 
+# During parallel testing CTest will not start a new test if doing
+# so would cause the system load to exceed this value.
+TestLoad: @CTEST_TEST_LOAD@
+
 UseLaunchers: @CTEST_USE_LAUNCHERS@
 CurlOptions: @CTEST_CURL_OPTIONS@
 # warning, if you add new options here that have to do with submit,
diff --git a/Source/CTest/cmCTestGenericHandler.cxx b/Source/CTest/cmCTestGenericHandler.cxx
index 81eb0a8..ad79ba2 100644
--- a/Source/CTest/cmCTestGenericHandler.cxx
+++ b/Source/CTest/cmCTestGenericHandler.cxx
@@ -23,6 +23,7 @@ cmCTestGenericHandler::cmCTestGenericHandler()
   this->SubmitIndex = 0;
   this->AppendXML = false;
   this->Quiet = false;
+  this->TestLoad = 0;
 }
 
 //----------------------------------------------------------------------
@@ -70,6 +71,7 @@ void cmCTestGenericHandler::SetPersistentOption(const std::string& op,
 void cmCTestGenericHandler::Initialize()
 {
   this->AppendXML = false;
+  this->TestLoad = 0;
   this->Options.clear();
   t_StringToString::iterator it;
   for ( it = this->PersistentOptions.begin();
diff --git a/Source/CTest/cmCTestGenericHandler.h b/Source/CTest/cmCTestGenericHandler.h
index 8567dd7..4b7ae79 100644
--- a/Source/CTest/cmCTestGenericHandler.h
+++ b/Source/CTest/cmCTestGenericHandler.h
@@ -89,6 +89,8 @@ public:
   void SetAppendXML(bool b) { this->AppendXML = b; }
   void SetQuiet(bool b) { this->Quiet = b; }
   bool GetQuiet() { return this->Quiet; }
+  void SetTestLoad(unsigned long load) { this->TestLoad = load; }
+  unsigned long GetTestLoad() const { return this->TestLoad;  }
 
 protected:
   bool StartResultingXML(cmCTest::Part part,
@@ -97,6 +99,7 @@ protected:
 
   bool AppendXML;
   bool Quiet;
+  unsigned long TestLoad;
   cmSystemTools::OutputOption HandlerVerbose;
   cmCTest *CTest;
   t_StringToString Options;
diff --git a/Source/CTest/cmCTestMultiProcessHandler.cxx b/Source/CTest/cmCTestMultiProcessHandler.cxx
index 28aec3d..4832186 100644
--- a/Source/CTest/cmCTestMultiProcessHandler.cxx
+++ b/Source/CTest/cmCTestMultiProcessHandler.cxx
@@ -13,12 +13,15 @@
 #include "cmProcess.h"
 #include "cmStandardIncludes.h"
 #include "cmCTest.h"
+#include "cmCTestScriptHandler.h"
 #include "cmSystemTools.h"
 #include <stdlib.h>
 #include <stack>
 #include <list>
 #include <float.h>
+#include <math.h>
 #include <cmsys/FStream.hxx>
+#include <cmsys/SystemInformation.hxx>
 
 class TestComparator
 {
@@ -40,6 +43,7 @@ private:
 cmCTestMultiProcessHandler::cmCTestMultiProcessHandler()
 {
   this->ParallelLevel = 1;
+  this->TestLoad = 0;
   this->Completed = 0;
   this->RunningCount = 0;
   this->StopTimePassed = false;
@@ -84,6 +88,11 @@ void cmCTestMultiProcessHandler::SetParallelLevel(size_t level)
   this->ParallelLevel = level < 1 ? 1 : level;
 }
 
+void cmCTestMultiProcessHandler::SetTestLoad(unsigned long load)
+{
+  this->TestLoad = load;
+}
+
 //---------------------------------------------------------
 void cmCTestMultiProcessHandler::RunTests()
 {
@@ -213,6 +222,11 @@ inline size_t cmCTestMultiProcessHandler::GetProcessorsUsed(int test)
   return processors;
 }
 
+std::string cmCTestMultiProcessHandler::GetName(int test)
+{
+  return this->Properties[test]->Name;
+}
+
 //---------------------------------------------------------
 bool cmCTestMultiProcessHandler::StartTest(int test)
 {
@@ -259,6 +273,46 @@ void cmCTestMultiProcessHandler::StartNextTests()
     return;
     }
 
+  bool allTestsFailedTestLoadCheck = false;
+  bool usedFakeLoadForTesting = false;
+  size_t minProcessorsRequired = this->ParallelLevel;
+  std::string testWithMinProcessors = "";
+
+  cmsys::SystemInformation info;
+
+  unsigned long systemLoad = 0;
+  size_t spareLoad = 0;
+  if (this->TestLoad > 0)
+    {
+    // Activate possible wait.
+    allTestsFailedTestLoadCheck = true;
+
+    // Check for a fake load average value used in testing.
+    if (const char* fake_load_value =
+        cmSystemTools::GetEnv("__CTEST_FAKE_LOAD_AVERAGE_FOR_TESTING"))
+      {
+      usedFakeLoadForTesting = true;
+      if (!cmSystemTools::StringToULong(fake_load_value, &systemLoad))
+        {
+        cmSystemTools::Error("Failed to parse fake load value: ",
+                             fake_load_value);
+        }
+      }
+    // If it's not set, look up the true load average.
+    else
+      {
+      systemLoad = static_cast<unsigned long>(ceil(info.GetLoadAverage()));
+      }
+    spareLoad = (this->TestLoad > systemLoad ?
+                 this->TestLoad - systemLoad : 0);
+
+    // Don't start more tests than the spare load can support.
+    if (numToStart > spareLoad)
+      {
+      numToStart = spareLoad;
+      }
+    }
+
   TestList copy = this->SortedTests;
   for(TestList::iterator test = copy.begin(); test != copy.end(); ++test)
     {
@@ -274,18 +328,74 @@ void cmCTestMultiProcessHandler::StartNextTests()
       }
 
     size_t processors = GetProcessorsUsed(*test);
+    bool testLoadOk = true;
+    if (this->TestLoad > 0)
+      {
+      if (processors <= spareLoad)
+        {
+        cmCTestLog(this->CTest, DEBUG,
+                    "OK to run " << GetName(*test) <<
+                    ", it requires " << processors <<
+                    " procs & system load is: " <<
+                    systemLoad << std::endl);
+        allTestsFailedTestLoadCheck = false;
+        }
+      else
+        {
+        testLoadOk = false;
+        }
+      }
 
-    if(processors <= numToStart && this->StartTest(*test))
+    if (processors <= minProcessorsRequired)
       {
-        if(this->StopTimePassed)
-          {
-          return;
-          }
-        numToStart -= processors;
+      minProcessorsRequired = processors;
+      testWithMinProcessors = GetName(*test);
+      }
+
+    if(testLoadOk && processors <= numToStart && this->StartTest(*test))
+      {
+      if(this->StopTimePassed)
+        {
+        return;
+        }
+
+      numToStart -= processors;
       }
     else if(numToStart == 0)
       {
-      return;
+      break;
+      }
+    }
+
+  if (allTestsFailedTestLoadCheck)
+    {
+    cmCTestLog(this->CTest, HANDLER_OUTPUT, "***** WAITING, ");
+    if (this->SerialTestRunning)
+      {
+      cmCTestLog(this->CTest, HANDLER_OUTPUT,
+                 "Waiting for RUN_SERIAL test to finish.");
+      }
+    else
+      {
+      cmCTestLog(this->CTest, HANDLER_OUTPUT,
+                 "System Load: " << systemLoad << ", "
+                 "Max Allowed Load: " << this->TestLoad << ", "
+                 "Smallest test " << testWithMinProcessors <<
+                 " requires " << minProcessorsRequired);
+      }
+    cmCTestLog(this->CTest, HANDLER_OUTPUT, "*****" << std::endl);
+
+    if (usedFakeLoadForTesting)
+      {
+      // Break out of the infinite loop of waiting for our fake load
+      // to come down.
+      this->StopTimePassed = true;
+      }
+    else
+      {
+      // Wait between 1 and 5 seconds before trying again.
+      cmCTestScriptHandler::SleepInSeconds(
+        cmSystemTools::RandomSeed() % 5 + 1);
       }
     }
 }
diff --git a/Source/CTest/cmCTestMultiProcessHandler.h b/Source/CTest/cmCTestMultiProcessHandler.h
index 243318f..ed3e155 100644
--- a/Source/CTest/cmCTestMultiProcessHandler.h
+++ b/Source/CTest/cmCTestMultiProcessHandler.h
@@ -37,6 +37,7 @@ public:
   void SetTests(TestMap& tests, PropertiesMap& properties);
   // Set the max number of tests that can be run at the same time.
   void SetParallelLevel(size_t);
+  void SetTestLoad(unsigned long load);
   virtual void RunTests();
   void PrintTestList();
   void PrintLabels();
@@ -93,6 +94,7 @@ protected:
   bool CheckCycles();
   int FindMaxIndex();
   inline size_t GetProcessorsUsed(int index);
+  std::string GetName(int index);
 
   void LockResources(int index);
   void UnlockResources(int index);
@@ -116,6 +118,7 @@ protected:
   std::set<std::string> LockedResources;
   std::vector<cmCTestTestHandler::cmCTestTestResult>* TestResults;
   size_t ParallelLevel; // max number of process that can be run at once
+  unsigned long TestLoad;
   std::set<cmCTestRunTest*> RunningTests;  // current running tests
   cmCTestTestHandler * TestHandler;
   cmCTest* CTest;
diff --git a/Source/CTest/cmCTestTestCommand.cxx b/Source/CTest/cmCTestTestCommand.cxx
index 8b357ac..b7d8318 100644
--- a/Source/CTest/cmCTestTestCommand.cxx
+++ b/Source/CTest/cmCTestTestCommand.cxx
@@ -26,6 +26,7 @@ cmCTestTestCommand::cmCTestTestCommand()
   this->Arguments[ctt_PARALLEL_LEVEL] = "PARALLEL_LEVEL";
   this->Arguments[ctt_SCHEDULE_RANDOM] = "SCHEDULE_RANDOM";
   this->Arguments[ctt_STOP_TIME] = "STOP_TIME";
+  this->Arguments[ctt_TEST_LOAD] = "TEST_LOAD";
   this->Arguments[ctt_LAST] = 0;
   this->Last = ctt_LAST;
 }
@@ -103,6 +104,38 @@ cmCTestGenericHandler* cmCTestTestCommand::InitializeHandler()
     {
     this->CTest->SetStopTime(this->Values[ctt_STOP_TIME]);
     }
+
+  // Test load is determined by: TEST_LOAD argument,
+  // or CTEST_TEST_LOAD script variable, or ctest --test-load
+  // command line argument... in that order.
+  unsigned long testLoad;
+  const char* ctestTestLoad
+    = this->Makefile->GetDefinition("CTEST_TEST_LOAD");
+  if(this->Values[ctt_TEST_LOAD] && *this->Values[ctt_TEST_LOAD])
+    {
+    if (!cmSystemTools::StringToULong(this->Values[ctt_TEST_LOAD], &testLoad))
+      {
+      testLoad = 0;
+      cmCTestLog(this->CTest, WARNING, "Invalid value for 'TEST_LOAD' : "
+          << this->Values[ctt_TEST_LOAD] << std::endl);
+      }
+    }
+  else if(ctestTestLoad && *ctestTestLoad)
+    {
+    if (!cmSystemTools::StringToULong(ctestTestLoad, &testLoad))
+      {
+      testLoad = 0;
+      cmCTestLog(this->CTest, WARNING,
+        "Invalid value for 'CTEST_TEST_LOAD' : " <<
+        ctestTestLoad << std::endl);
+      }
+    }
+  else
+    {
+    testLoad = this->CTest->GetTestLoad();
+    }
+  handler->SetTestLoad(testLoad);
+
   handler->SetQuiet(this->Quiet);
   return handler;
 }
diff --git a/Source/CTest/cmCTestTestCommand.h b/Source/CTest/cmCTestTestCommand.h
index a1e5f36..0dfca97 100644
--- a/Source/CTest/cmCTestTestCommand.h
+++ b/Source/CTest/cmCTestTestCommand.h
@@ -60,6 +60,7 @@ protected:
     ctt_PARALLEL_LEVEL,
     ctt_SCHEDULE_RANDOM,
     ctt_STOP_TIME,
+    ctt_TEST_LOAD,
     ctt_LAST
   };
 };
diff --git a/Source/CTest/cmCTestTestHandler.cxx b/Source/CTest/cmCTestTestHandler.cxx
index 70b7f5c..59576f4 100644
--- a/Source/CTest/cmCTestTestHandler.cxx
+++ b/Source/CTest/cmCTestTestHandler.cxx
@@ -1062,6 +1062,14 @@ void cmCTestTestHandler::ProcessDirectory(std::vector<std::string> &passed,
   parallel->SetParallelLevel(this->CTest->GetParallelLevel());
   parallel->SetTestHandler(this);
   parallel->SetQuiet(this->Quiet);
+  if(this->TestLoad > 0)
+    {
+    parallel->SetTestLoad(this->TestLoad);
+    }
+  else
+    {
+    parallel->SetTestLoad(this->CTest->GetTestLoad());
+    }
 
   *this->LogFile << "Start testing: "
     << this->CTest->CurrentTime() << std::endl
diff --git a/Source/cmCTest.cxx b/Source/cmCTest.cxx
index e3b7a2b..5887ba8 100644
--- a/Source/cmCTest.cxx
+++ b/Source/cmCTest.cxx
@@ -294,6 +294,7 @@ cmCTest::cmCTest()
   this->LabelSummary           = true;
   this->ParallelLevel          = 1;
   this->ParallelLevelSetInCli  = false;
+  this->TestLoad               = 0;
   this->SubmitIndex            = 0;
   this->Failover               = false;
   this->BatchJobs              = false;
@@ -393,6 +394,11 @@ void cmCTest::SetParallelLevel(int level)
   this->ParallelLevel = level < 1 ? 1 : level;
 }
 
+void cmCTest::SetTestLoad(unsigned long load)
+{
+  this->TestLoad = load;
+}
+
 //----------------------------------------------------------------------------
 bool cmCTest::ShouldCompressTestOutput()
 {
@@ -820,6 +826,20 @@ bool cmCTest::UpdateCTestConfiguration()
     cmSystemTools::ChangeDirectory(this->BinaryDir);
     }
   this->TimeOut = atoi(this->GetCTestConfiguration("TimeOut").c_str());
+  std::string const& testLoad = this->GetCTestConfiguration("TestLoad");
+  if (!testLoad.empty())
+    {
+    unsigned long load;
+    if (cmSystemTools::StringToULong(testLoad.c_str(), &load))
+      {
+      this->SetTestLoad(load);
+      }
+    else
+      {
+      cmCTestLog(this, WARNING, "Invalid value for 'Test Load' : "
+          << testLoad << std::endl);
+      }
+    }
   if ( this->ProduceXML )
     {
     this->CompressXMLFiles = cmSystemTools::IsOn(
@@ -2051,6 +2071,21 @@ bool cmCTest::HandleCommandLineArguments(size_t &i,
       }
     }
 
+  if(this->CheckArgument(arg, "--test-load") && i < args.size() - 1)
+    {
+    i++;
+    unsigned long load;
+    if (cmSystemTools::StringToULong(args[i].c_str(), &load))
+      {
+      this->SetTestLoad(load);
+      }
+    else
+      {
+      cmCTestLog(this, WARNING,
+                 "Invalid value for 'Test Load' : " << args[i] << std::endl);
+      }
+    }
+
   if(this->CheckArgument(arg, "--no-compress-output"))
     {
     this->CompressTestOutput = false;
diff --git a/Source/cmCTest.h b/Source/cmCTest.h
index db3ea10..47245ae 100644
--- a/Source/cmCTest.h
+++ b/Source/cmCTest.h
@@ -161,6 +161,9 @@ public:
   int GetParallelLevel() { return this->ParallelLevel; }
   void SetParallelLevel(int);
 
+  unsigned long GetTestLoad() { return this->TestLoad; }
+  void SetTestLoad(unsigned long);
+
   /**
    * Check if CTest file exists
    */
@@ -499,6 +502,8 @@ private:
   int                     ParallelLevel;
   bool                    ParallelLevelSetInCli;
 
+  unsigned long           TestLoad;
+
   int                     CompatibilityMode;
 
   // information for the --build-and-test options
diff --git a/Source/ctest.cxx b/Source/ctest.cxx
index e784759..afcbd61 100644
--- a/Source/ctest.cxx
+++ b/Source/ctest.cxx
@@ -98,6 +98,7 @@ static const char * cmDocumentationOptions[][2] =
 
   {"--test-command", "The test to run with the --build-and-test option."},
   {"--test-timeout", "The time limit in seconds, internal use only."},
+  {"--test-load", "CPU load threshold for starting new parallel tests."},
   {"--tomorrow-tag", "Nightly or experimental starts with next day tag."},
   {"--ctest-config", "The configuration file used to initialize CTest state "
    "when submitting dashboards."},
diff --git a/Tests/RunCMake/CTestCommandLine/RunCMakeTest.cmake b/Tests/RunCMake/CTestCommandLine/RunCMakeTest.cmake
index a3ce139..aba1daf 100644
--- a/Tests/RunCMake/CTestCommandLine/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CTestCommandLine/RunCMakeTest.cmake
@@ -1,4 +1,5 @@
 include(RunCMake)
+set(RunCMake_TEST_TIMEOUT 60)
 
 unset(ENV{CTEST_PARALLEL_LEVEL})
 unset(ENV{CTEST_OUTPUT_ON_FAILURE})
@@ -52,3 +53,35 @@ add_test(MergeOutput \"${CMAKE_COMMAND}\" -P \"${RunCMake_SOURCE_DIR}/MergeOutpu
   run_cmake_command(MergeOutput ${CMAKE_CTEST_COMMAND} -V)
 endfunction()
 run_MergeOutput()
+
+
+function(run_TestLoad name load)
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/TestLoad)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+  file(WRITE "${RunCMake_TEST_BINARY_DIR}/CTestTestfile.cmake" "
+  add_test(TestLoad1 \"${CMAKE_COMMAND}\" -E echo \"test of --test-load\")
+  add_test(TestLoad2 \"${CMAKE_COMMAND}\" -E echo \"test of --test-load\")
+")
+  run_cmake_command(${name} ${CMAKE_CTEST_COMMAND} -j2 --test-load ${load} --test-timeout 5)
+endfunction()
+
+# Tests for the --test-load feature of ctest
+#
+# Spoof a load average value to make these tests more reliable.
+set(ENV{__CTEST_FAKE_LOAD_AVERAGE_FOR_TESTING} 5)
+
+# Verify that new tests are not started when the load average exceeds
+# our threshold.
+run_TestLoad(test-load-fail 2)
+
+# Verify that warning message is displayed but tests still start when
+# an invalid argument is given.
+run_TestLoad(test-load-invalid 'two')
+
+# Verify that new tests are started when the load average falls below
+# our threshold.
+run_TestLoad(test-load-pass 10)
+
+unset(ENV{__CTEST_FAKE_LOAD_AVERAGE_FOR_TESTING})
diff --git a/Tests/RunCMake/CTestCommandLine/test-load-fail-stderr.txt b/Tests/RunCMake/CTestCommandLine/test-load-fail-stderr.txt
new file mode 100644
index 0000000..eafba1c
--- /dev/null
+++ b/Tests/RunCMake/CTestCommandLine/test-load-fail-stderr.txt
@@ -0,0 +1 @@
+No tests were found!!!
diff --git a/Tests/RunCMake/CTestCommandLine/test-load-fail-stdout.txt b/Tests/RunCMake/CTestCommandLine/test-load-fail-stdout.txt
new file mode 100644
index 0000000..153da09
--- /dev/null
+++ b/Tests/RunCMake/CTestCommandLine/test-load-fail-stdout.txt
@@ -0,0 +1,2 @@
+^Test project .*/Tests/RunCMake/CTestCommandLine/TestLoad
+\*\*\*\*\* WAITING, System Load: 5, Max Allowed Load: 2, Smallest test TestLoad[1-2] requires 1\*\*\*\*\*
diff --git a/Tests/RunCMake/CTestCommandLine/test-load-invalid-stderr.txt b/Tests/RunCMake/CTestCommandLine/test-load-invalid-stderr.txt
new file mode 100644
index 0000000..caab3b9
--- /dev/null
+++ b/Tests/RunCMake/CTestCommandLine/test-load-invalid-stderr.txt
@@ -0,0 +1 @@
+Invalid value for 'Test Load' : 'two'
diff --git a/Tests/RunCMake/CTestCommandLine/test-load-invalid-stdout.txt b/Tests/RunCMake/CTestCommandLine/test-load-invalid-stdout.txt
new file mode 100644
index 0000000..7ee3dae
--- /dev/null
+++ b/Tests/RunCMake/CTestCommandLine/test-load-invalid-stdout.txt
@@ -0,0 +1,7 @@
+^Test project .*/Tests/RunCMake/CTestCommandLine/TestLoad
+    Start 1: TestLoad1
+    Start 2: TestLoad2
+1/2 Test #[1-2]: TestLoad[1-2] ........................   Passed +[0-9.]+ sec
+2/2 Test #[1-2]: TestLoad[1-2] ........................   Passed +[0-9.]+ sec
++
+100% tests passed, 0 tests failed out of 2
diff --git a/Tests/RunCMake/CTestCommandLine/test-load-pass-stderr.txt b/Tests/RunCMake/CTestCommandLine/test-load-pass-stderr.txt
new file mode 100644
index 0000000..10f3293
--- /dev/null
+++ b/Tests/RunCMake/CTestCommandLine/test-load-pass-stderr.txt
@@ -0,0 +1 @@
+^$
diff --git a/Tests/RunCMake/CTestCommandLine/test-load-pass-stdout.txt b/Tests/RunCMake/CTestCommandLine/test-load-pass-stdout.txt
new file mode 100644
index 0000000..7ee3dae
--- /dev/null
+++ b/Tests/RunCMake/CTestCommandLine/test-load-pass-stdout.txt
@@ -0,0 +1,7 @@
+^Test project .*/Tests/RunCMake/CTestCommandLine/TestLoad
+    Start 1: TestLoad1
+    Start 2: TestLoad2
+1/2 Test #[1-2]: TestLoad[1-2] ........................   Passed +[0-9.]+ sec
+2/2 Test #[1-2]: TestLoad[1-2] ........................   Passed +[0-9.]+ sec
++
+100% tests passed, 0 tests failed out of 2
diff --git a/Tests/RunCMake/ctest_test/CTestTestLoadFail-result.txt b/Tests/RunCMake/ctest_test/CTestTestLoadFail-result.txt
new file mode 100644
index 0000000..b57e2de
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/CTestTestLoadFail-result.txt
@@ -0,0 +1 @@
+(-1|255)
diff --git a/Tests/RunCMake/ctest_test/CTestTestLoadFail-stderr.txt b/Tests/RunCMake/ctest_test/CTestTestLoadFail-stderr.txt
new file mode 100644
index 0000000..eafba1c
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/CTestTestLoadFail-stderr.txt
@@ -0,0 +1 @@
+No tests were found!!!
diff --git a/Tests/RunCMake/ctest_test/CTestTestLoadFail-stdout.txt b/Tests/RunCMake/ctest_test/CTestTestLoadFail-stdout.txt
new file mode 100644
index 0000000..e203c10
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/CTestTestLoadFail-stdout.txt
@@ -0,0 +1,2 @@
+Test project .*/Tests/RunCMake/ctest_test/CTestTestLoadFail-build
+\*\*\*\*\* WAITING, System Load: 5, Max Allowed Load: 4, Smallest test RunCMakeVersion requires 1\*\*\*\*\*$
diff --git a/Tests/RunCMake/ctest_test/CTestTestLoadInvalid-stderr.txt b/Tests/RunCMake/ctest_test/CTestTestLoadInvalid-stderr.txt
new file mode 100644
index 0000000..7f2d7f6
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/CTestTestLoadInvalid-stderr.txt
@@ -0,0 +1 @@
+^Invalid value for 'CTEST_TEST_LOAD' : ERR2
diff --git a/Tests/RunCMake/ctest_test/CTestTestLoadInvalid-stdout.txt b/Tests/RunCMake/ctest_test/CTestTestLoadInvalid-stdout.txt
new file mode 100644
index 0000000..b54220c
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/CTestTestLoadInvalid-stdout.txt
@@ -0,0 +1,7 @@
+Test project .*/Tests/RunCMake/ctest_test/CTestTestLoadInvalid-build
+    Start 1: RunCMakeVersion
+1/1 Test #1: RunCMakeVersion ..................   Passed +[0-9.]+ sec
++
+100% tests passed, 0 tests failed out of 1
++
+Total Test time \(real\) = +[0-9.]+ sec$
diff --git a/Tests/RunCMake/ctest_test/CTestTestLoadPass-stdout.txt b/Tests/RunCMake/ctest_test/CTestTestLoadPass-stdout.txt
new file mode 100644
index 0000000..c221eed
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/CTestTestLoadPass-stdout.txt
@@ -0,0 +1,7 @@
+Test project .*/Tests/RunCMake/ctest_test/CTestTestLoadPass-build
+    Start 1: RunCMakeVersion
+1/1 Test #1: RunCMakeVersion ..................   Passed +[0-9.]+ sec
++
+100% tests passed, 0 tests failed out of 1
++
+Total Test time \(real\) = +[0-9.]+ sec$
diff --git a/Tests/RunCMake/ctest_test/RunCMakeTest.cmake b/Tests/RunCMake/ctest_test/RunCMakeTest.cmake
index d906290..21d0447 100644
--- a/Tests/RunCMake/ctest_test/RunCMakeTest.cmake
+++ b/Tests/RunCMake/ctest_test/RunCMakeTest.cmake
@@ -1,6 +1,8 @@
 include(RunCTest)
+set(RunCMake_TEST_TIMEOUT 60)
 
 set(CASE_CTEST_TEST_ARGS "")
+set(CASE_CTEST_TEST_LOAD "")
 
 function(run_ctest_test CASE_NAME)
   set(CASE_CTEST_TEST_ARGS "${ARGN}")
@@ -8,3 +10,42 @@ function(run_ctest_test CASE_NAME)
 endfunction()
 
 run_ctest_test(TestQuiet QUIET)
+
+# Tests for the 'Test Load' feature of ctest
+#
+# Spoof a load average value to make these tests more reliable.
+set(ENV{__CTEST_FAKE_LOAD_AVERAGE_FOR_TESTING} 5)
+
+# Verify that new tests are started when the load average falls below
+# our threshold.
+run_ctest_test(TestLoadPass TEST_LOAD 6)
+
+# Verify that new tests are not started when the load average exceeds
+# our threshold.
+run_ctest_test(TestLoadFail TEST_LOAD 2)
+
+# Verify that when an invalid "TEST_LOAD" value is given, a warning
+# message is displayed and the value is ignored.
+run_ctest_test(TestLoadInvalid TEST_LOAD "ERR1")
+
+# Verify that new tests are started when the load average falls below
+# our threshold.
+set(CASE_CTEST_TEST_LOAD 7)
+run_ctest_test(CTestTestLoadPass)
+
+# Verify that new tests are not started when the load average exceeds
+# our threshold.
+set(CASE_CTEST_TEST_LOAD 4)
+run_ctest_test(CTestTestLoadFail)
+
+# Verify that when an invalid "CTEST_TEST_LOAD" value is given,
+# a warning message is displayed and the value is ignored.
+set(CASE_CTEST_TEST_LOAD "ERR2")
+run_ctest_test(CTestTestLoadInvalid)
+
+# Verify that the "TEST_LOAD" value has higher precedence than
+# the "CTEST_TEST_LOAD" value
+set(CASE_CTEST_TEST_LOAD "ERR3")
+run_ctest_test(TestLoadOrder TEST_LOAD "ERR4")
+
+unset(ENV{__CTEST_FAKE_LOAD_AVERAGE_FOR_TESTING})
diff --git a/Tests/RunCMake/ctest_test/TestLoadFail-result.txt b/Tests/RunCMake/ctest_test/TestLoadFail-result.txt
new file mode 100644
index 0000000..b57e2de
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadFail-result.txt
@@ -0,0 +1 @@
+(-1|255)
diff --git a/Tests/RunCMake/ctest_test/TestLoadFail-stderr.txt b/Tests/RunCMake/ctest_test/TestLoadFail-stderr.txt
new file mode 100644
index 0000000..eafba1c
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadFail-stderr.txt
@@ -0,0 +1 @@
+No tests were found!!!
diff --git a/Tests/RunCMake/ctest_test/TestLoadFail-stdout.txt b/Tests/RunCMake/ctest_test/TestLoadFail-stdout.txt
new file mode 100644
index 0000000..4d7ce48
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadFail-stdout.txt
@@ -0,0 +1,2 @@
+Test project .*/Tests/RunCMake/ctest_test/TestLoadFail-build
+\*\*\*\*\* WAITING, System Load: 5, Max Allowed Load: 2, Smallest test RunCMakeVersion requires 1\*\*\*\*\*$
diff --git a/Tests/RunCMake/ctest_test/TestLoadInvalid-stderr.txt b/Tests/RunCMake/ctest_test/TestLoadInvalid-stderr.txt
new file mode 100644
index 0000000..40ddb3a
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadInvalid-stderr.txt
@@ -0,0 +1 @@
+^Invalid value for 'TEST_LOAD' : ERR1
diff --git a/Tests/RunCMake/ctest_test/TestLoadInvalid-stdout.txt b/Tests/RunCMake/ctest_test/TestLoadInvalid-stdout.txt
new file mode 100644
index 0000000..c4fd35b
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadInvalid-stdout.txt
@@ -0,0 +1,7 @@
+Test project .*/Tests/RunCMake/ctest_test/TestLoadInvalid-build
+    Start 1: RunCMakeVersion
+1/1 Test #1: RunCMakeVersion ..................   Passed +[0-9.]+ sec
++
+100% tests passed, 0 tests failed out of 1
++
+Total Test time \(real\) = +[0-9.]+ sec$
diff --git a/Tests/RunCMake/ctest_test/TestLoadOrder-stderr.txt b/Tests/RunCMake/ctest_test/TestLoadOrder-stderr.txt
new file mode 100644
index 0000000..1de730e
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadOrder-stderr.txt
@@ -0,0 +1 @@
+^Invalid value for 'TEST_LOAD' : ERR4
diff --git a/Tests/RunCMake/ctest_test/TestLoadOrder-stdout.txt b/Tests/RunCMake/ctest_test/TestLoadOrder-stdout.txt
new file mode 100644
index 0000000..22da092
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadOrder-stdout.txt
@@ -0,0 +1,7 @@
+Test project .*/Tests/RunCMake/ctest_test/TestLoadOrder-build
+    Start 1: RunCMakeVersion
+1/1 Test #1: RunCMakeVersion ..................   Passed +[0-9.]+ sec
++
+100% tests passed, 0 tests failed out of 1
++
+Total Test time \(real\) = +[0-9.]+ sec$
diff --git a/Tests/RunCMake/ctest_test/TestLoadPass-stdout.txt b/Tests/RunCMake/ctest_test/TestLoadPass-stdout.txt
new file mode 100644
index 0000000..e5048f4
--- /dev/null
+++ b/Tests/RunCMake/ctest_test/TestLoadPass-stdout.txt
@@ -0,0 +1,7 @@
+Test project .*/Tests/RunCMake/ctest_test/TestLoadPass-build
+    Start 1: RunCMakeVersion
+1/1 Test #1: RunCMakeVersion ..................   Passed +[0-9.]+ sec
++
+100% tests passed, 0 tests failed out of 1
++
+Total Test time \(real\) = +[0-9.]+ sec$
diff --git a/Tests/RunCMake/ctest_test/test.cmake.in b/Tests/RunCMake/ctest_test/test.cmake.in
index 1350abe..a8de6a3 100644
--- a/Tests/RunCMake/ctest_test/test.cmake.in
+++ b/Tests/RunCMake/ctest_test/test.cmake.in
@@ -8,6 +8,7 @@ set(CTEST_CMAKE_GENERATOR               "@RunCMake_GENERATOR@")
 set(CTEST_CMAKE_GENERATOR_PLATFORM      "@RunCMake_GENERATOR_PLATFORM@")
 set(CTEST_CMAKE_GENERATOR_TOOLSET       "@RunCMake_GENERATOR_TOOLSET@")
 set(CTEST_BUILD_CONFIGURATION           "$ENV{CMAKE_CONFIG_TYPE}")
+set(CTEST_TEST_LOAD                     "@CASE_CTEST_TEST_LOAD@")
 
 set(ctest_test_args "@CASE_CTEST_TEST_ARGS@")
 ctest_start(Experimental)