build: turn on package parallel builds by default and fix descriptions.

By default, this is only used when building with make -j.

SVN-Revision: 33582

Config.in

@@ -296,23 +296,12 @@ menu "Global build settings"
 	config PKG_BUILD_PARALLEL
 		bool
 		prompt "Compile certain packages parallelized"
-		default n
+		default y
 		help
 		  This adds a -jX option to certain packages that are known to
-		  behave well for parallel build.
+		  behave well for parallel build. By default the package make processes
-
+		  use the main jobserver, in which case this option only takes effect
-		  Note that this may overcommit CPU resources depending on the
+		  when you add -jX to the make command.
-		  -j level of the main make process, the number of package
-		  submake jobs selected below and the number of actual CPUs present.
-		  Example: If the main make is passed a -j4 and the submake -j
-		  is also set to 4, we may end up with 16 parallel make processes
-		  in the worst case.
-
-		  You get maximum build performance, if you set the package build
-		  jobs to the number of CPUs (cores) available and also start the main
-		  make process with -jX, where X is the number of CPUs (cores).
-		  However, make sure you have enough RAM available for
-		  NR_CPUS to the power of two (NR_CPUS^2) make jobs.
 
 		  If you are unsure, select N.
 
@@ -325,6 +314,14 @@ menu "Global build settings"
 		  This passes the main make process jobserver fds to package builds,
 		  enabling full parallelization across different packages
 
+		  Note that disabling this may overcommit CPU resources depending on the
+		  -j level of the main make process, the number of package
+		  submake jobs selected below and the number of actual CPUs present.
+		  Example: If the main make is passed a -j4 and the submake -j
+		  is also set to 4, we may end up with 16 parallel make processes
+		  in the worst case.
+
+
 	config PKG_BUILD_JOBS
 		int
 		prompt "Number of package submake jobs (2-512)"