doc: more explanation about hwloc

doc/chapters/configuration.texi

@@ -46,6 +46,16 @@ any value.
 @item --enable-coverage
 Enable flags for the @code{gcov} coverage tool.
 
+@item --with-hwloc
+Specify hwloc should be used by StarPU. hwloc should be found by the
+means of the tools @code{pkg-config}.
+
+@item --with-hwloc=@var{prefix}
+Specify hwloc should be used by StarPU. hwloc should be found in the
+directory specified by @var{prefix}.
+
+@item --without-hwloc
+Specify hwloc should not be used by StarPU.
 @end table
 
 Additionally, the @command{configure} script recognize many variables, which

doc/chapters/installing.texi

@@ -58,6 +58,13 @@ recommended.  It allows for topology aware scheduling, which improves
 performance.  @code{hwloc} is available in major free operating system
 distributions, and for most operating systems.
 
+If hwloc is not available on your system, the option
+@code{--without-hwloc} should be explicitely given when calling the
+configure script. If hwloc is installed with a @code{pkg-config} file,
+no option is required, it will be detected automatically, otherwise
+the @code{with-hwloc=prefix} should be used to specified the location
+of hwloc.
+
 @node Configuration of StarPU
 @section Configuration of StarPU