mlr: enlarging the documentation, explaining the additional output and the analysis script

doc/doxygen/chapters/370_online_performance_tools.doxy

@@ -414,7 +414,7 @@ creation. These need to be extracted by the <c>cl_perf_func</c>
 function, which should be defined by the user. \f$\alpha, \beta,
 \gamma\f$ are the exponents defined by the user in
 <c>model->combinations</c> table. Finally, coefficients \f$a, b, c\f$
-are computed automatically at the end of the execution, using least
+are computed automatically by the StarPU at the end of the execution, using least
 squares method of the <c>dgels_</c> LAPACK function.
 
 <c>examples/mlr/mlr.c</c> example provides more details on
@@ -424,9 +424,17 @@ Coefficients computation is done at the end of the execution, and the
 results are stored in standard codelet perfmodel files. Additional
 files containing the duration of task together with the value of each
 parameter are stored in <c>.starpu/sampling/codelets/tmp/</c>
-directory. These files are reused when \ref STARPU_CALIBRATE environment
-variable is set to <c>1</c>, to recompute coefficients based on the current,
-but also on the previous executions.
+directory. These files are reused when \ref STARPU_CALIBRATE
+environment variable is set to <c>1</c>, to recompute coefficients
+based on the current, but also on the previous
+executions. Additionally, when multiple linear regression models are
+disabled (using "--disable-mlr" configuration option) or when the
+<c>model->combinations</c> are not defined, StarPU will still write
+output files into <c>.starpu/sampling/codelets/tmp/</c> to allow
+performing an analysis. This analysis typically aims at finding the
+most appropriate equation for the codelet and
+<c>tools/starpu_mlr_analysis</c> script provides an example of how to
+perform such study.
 
 </li>