Merge pull request #5990 from tjhei/step-37-print-vec-info

step-37: print vectorization info

doc/news/changes/minor/20180421Heister

@@ -0,0 +1,3 @@
+New: Utilities::System::get_current_vectorization_level() returns the currently used vectorization support in string format.
+<br>
+(Timo Heister, 2018/04/21)

examples/step-37/doc/intro.dox

@@ -514,7 +514,8 @@ FEEvaluation for your computer, you should compile deal.II with the so-called
 enabled by setting the variable <tt>CMAKE_CXX_FLAGS</tt> to
 <tt>"-march=native"</tt> in the cmake build settings (on the command line,
 specify <tt>-DCMAKE_CXX_FLAGS="-march=native"</tt>, see the deal.II README for
-more information). Similar options exist for other compilers.
+more information). Similar options exist for other compilers. We output
+the current vectorization length in the run() function of this example.
 
 
 <h3>Running multigrid on large-scale parallel computers</h3>

examples/step-37/doc/results.dox

@@ -13,6 +13,7 @@ Of more interest is to evaluate some aspects of the multigrid solver.
 When we run this program in 2D for quadratic ($Q_2$) elements, we get the
 following output (when run on one core in release mode):
 @code
+Vectorization over 2 doubles = 128 bits (SSE2), VECTORIZATION_LEVEL=1
 Cycle 0
 Number of degrees of freedom: 81
 Total setup time               (wall) 0.00159788s
@@ -67,6 +68,7 @@ use uniform mesh refinement, we get eight times as many elements and
 approximately eight times as many degrees of freedom with each cycle:
 
 @code
+Vectorization over 2 doubles = 128 bits (SSE2), VECTORIZATION_LEVEL=1
 Cycle 0
 Number of degrees of freedom: 125
 Total setup time               (wall) 0.00231099s
@@ -105,6 +107,7 @@ degree_finite_element=4;</code> at the top of the program, we get the
 following program output:
 
 @code
+Vectorization over 2 doubles = 128 bits (SSE2), VECTORIZATION_LEVEL=1
 Cycle 0
 Number of degrees of freedom: 729
 Total setup time               (wall) 0.00633097s
@@ -157,6 +160,7 @@ Finally, let us look at the timings with degree 8, which corresponds to
 another round of mesh refinement in the lower order methods:
 
 @code
+Vectorization over 2 doubles = 128 bits (SSE2), VECTORIZATION_LEVEL=1
 Cycle 0
 Number of degrees of freedom: 4913
 Total setup time               (wall) 0.0842004s

examples/step-37/step-37.cc

@@ -1159,9 +1159,22 @@ namespace Step37
   // The function that runs the program is very similar to the one in
   // step-16. We do few refinement steps in 3D compared to 2D, but that's
   // it.
+  //
+  // Before we run the program, we output some information about the detected
+  // vectorization level as discussed in the introduction.
   template <int dim>
   void LaplaceProblem<dim>::run ()
   {
+    {
+      const unsigned int n_vect_doubles = VectorizedArray<double>::n_array_elements;
+      const unsigned int n_vect_bits = 8*sizeof(double)*n_vect_doubles;
+
+      pcout << "Vectorization over " << n_vect_doubles
+            << " doubles = " << n_vect_bits << " bits ("
+            << Utilities::System::get_current_vectorization_level()
+            << "), VECTORIZATION_LEVEL=" << DEAL_II_COMPILER_VECTORIZATION_LEVEL << std::endl;
+    }
+
     for (unsigned int cycle=0; cycle<9-dim; ++cycle)
       {
         pcout << "Cycle " << cycle << std::endl;

include/deal.II/base/utilities.h

@@ -621,6 +621,40 @@ namespace Utilities
      */
     double get_cpu_load ();
 
+    /**
+     * Return the current level of vectorization as described by DEAL_II_COMPILER_VECTORIZATION_LEVEL
+     * in vectorization.h as a string. The list of possible return values is:
+     *
+     * <table>
+     * <tr>
+     *   <td><tt>VECTORIZATION_LEVEL</tt></td>
+     *   <td>Return Value</td>
+     *   <td>Width in bits</td>
+     * </tr>
+     * <tr>
+     *   <td>0</td>
+     *   <td>disabled</td>
+     *   <td>64</td>
+     * </tr>
+     * <tr>
+     *   <td>1</td>
+     *   <td>SSE2</td>
+     *   <td>128</td>
+     * </tr>
+     * <tr>
+     *   <td>2</td>
+     *   <td>AVX</td>
+     *   <td>256</td>
+     * </tr>
+     * <tr>
+     *   <td>3</td>
+     *   <td>AVX512</td>
+     *   <td>512</td>
+     * </tr>
+     * </table>
+     */
+    const std::string get_current_vectorization_level();
+
     /**
      * Structure that hold information about memory usage in kB. Used by
      * get_memory_stats(). See man 5 proc entry /status for details.

source/base/utilities.cc

@@ -631,6 +631,24 @@ namespace Utilities
 
 #endif
 
+    const std::string
+    get_current_vectorization_level()
+    {
+      switch (DEAL_II_COMPILER_VECTORIZATION_LEVEL)
+        {
+        case 0:
+          return "disabled";
+        case 1:
+          return "SSE2";
+        case 2:
+          return "AVX";
+        case 3:
+          return "AVX512";
+        default:
+          AssertThrow(false, ExcInternalError("Invalid DEAL_II_COMPILER_VECTORIZATION_LEVEL."));
+          return "ERROR";
+        }
+    }
 
 
     void get_memory_stats (MemoryStats &stats)