doc: add missing documentation

doc/chapters/basic-api.texi

@@ -2405,11 +2405,15 @@ Converts the given timespec @var{ts} into microseconds.
 @end deftypefun
 
 @deftypefun void starpu_bus_profiling_helper_display_summary (void)
-Displays statistics about the bus on stderr.
+Displays statistics about the bus on stderr. if the  environment
+variable @code{STARPU_BUS_STATS} is defined. The function is called
+automatically by @code{starpu_shutdown()}.
 @end deftypefun
 
 @deftypefun void starpu_worker_profiling_helper_display_summary (void)
-Displays statistics about the workers on stderr.
+Displays statistics about the workers on stderr if the environment
+variable @code{STARPU_WORKER_STATS} is defined. The function is called
+automatically by @code{starpu_shutdown()}.
 @end deftypefun
 
 @node CUDA extensions

doc/chapters/configuration.texi

@@ -539,10 +539,20 @@ as it emulates devices that have a limited amount of memory.
 
 @defvr {Environment variable} STARPU_GENERATE_TRACE
 When set to 1, this variable indicates that StarPU should automatically
-generate a Paje trace when starpu_shutdown is called.
+generate a Paje trace when @code{starpu_shutdown()} is called.
 @end defvr
 
 @defvr {Environment variable} STARPU_MEMORY_STATUS
 Enable the display of memory status at the end of the execution
 (@pxref{Memory feedback}).
 @end defvr
+
+@defvr {Environment variable} STARPU_BUS_STATS
+When defined, statistics about the bus will be displayed when calling
+@code{starpu_shutdown()} (@pxref{Execution statistics}).
+@end defvr
+
+@defvr {Environment variable} STARPU_WORKER_STATS
+When defined, statistics about the workers will be displayed when calling
+@code{starpu_shutdown()} (@pxref{Execution statistics}).
+@end defvr

doc/chapters/perf-feedback.texi

@@ -12,6 +12,7 @@
 * Codelet performance::         Performance of codelets
 * Theoretical lower bound on execution time API::  
 * Memory feedback::             
+* Execution statistics::        
 @end menu
 
 @node On-line
@@ -492,3 +493,14 @@ Node #3
 	Loaded (Shared) : 0
 	Invalidated (was Owner) : 0
 @end example
+
+@node Execution statistics
+@section Execution statistics
+
+Different statistics can be displayed at the end of the execution of
+the application. To enable them, you need to pass the option
+@code{--enable-statistics} when calling @code{configure} and/or set
+the environment variables @code{STARPU_BUS_STATS} and
+@code{STARPU_WORKER_STATS} when calling your application.
+
+