Document that we actually create several workers, but use only one at a time

doc/chapters/advanced-examples.texi

@@ -715,11 +715,10 @@ Other parallel libraries are also not safe when being invoked concurrently
 from different threads, due to the use of global variables in their sequential
 sections for instance.
 
-The solution is then to use only a single combined worker, scoping all
-the CPUs.  This can be done by setting @code{single_combined_worker}
-to 1 in the @code{starpu_conf} structure, or setting the
-@code{STARPU_SINGLE_COMBINED_WORKER} environment variable to 1. StarPU will then
-use parallel tasks only over all the CPUs at the same time.
+The solution is then to use only one combined worker at a time.  This can be
+done by setting @code{single_combined_worker} to 1 in the @code{starpu_conf}
+structure, or setting the @code{STARPU_SINGLE_COMBINED_WORKER} environment
+variable to 1. StarPU will then run only one parallel task at a time.
 
 @node Debugging
 @section Debugging

doc/chapters/basic-api.texi

@@ -109,11 +109,10 @@ executing tasks. If this value is equal to -1, the default value is used. This
 can also be specified with the @code{STARPU_CALIBRATE} environment variable.
 
 @item @code{int single_combined_worker} (default = 0)
-By default, StarPU creates various combined workers according to the machine
-structure. Some parallel libraries (e.g. most OpenMP implementations) however do
+By default, StarPU parallel tasks concurrently.
+Some parallel libraries (e.g. most OpenMP implementations) however do
 not support concurrent calls to parallel code. In such case, setting this flag
-makes StarPU only create one combined worker, containing all
-the CPU workers. This can also be specified by the
+makes StarPU only start one parallel task at a time.
 @code{STARPU_SINGLE_COMBINED_WORKER} environment variable.
 @end table
 @end deftp