context_tracking: Remove full dynticks' hacky dependency on wide context tracking

Now that the full dynticks subsystem only enables the context tracking
on full dynticks CPUs, lets remove the dependency on CONTEXT_TRACKING_FORCE

This dependency was a hack to enable the context tracking widely for the
full dynticks susbsystem until the latter becomes able to enable it in a
more CPU-finegrained fashion.

Now CONTEXT_TRACKING_FORCE only stands for testing on archs that
work on support for the context tracking while full dynticks can't be
used yet due to unmet dependencies. It simulates a system where all CPUs
are full dynticks so that RCU user extended quiescent states and dynticks
cputime accounting can be tested on the given arch.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>

1 files changed, 22 insertions, 6 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 247084be0590..ffbf5d788bf3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -527,13 +527,29 @@ config RCU_USER_QS
 config CONTEXT_TRACKING_FORCE
         bool "Force context tracking"
         depends on CONTEXT_TRACKING
-        default CONTEXT_TRACKING
+        default y if !NO_HZ_FULL
         help
-          Probe on user/kernel boundaries by default in order to
-          test the features that rely on it such as userspace RCU extended
-          quiescent states.
-          This test is there for debugging until we have a real user like the
-          full dynticks mode.
+          The major pre-requirement for full dynticks to work is to
+          support the context tracking subsystem. But there are also
+          other dependencies to provide in order to make the full
+          dynticks working.
+
+          This option stands for testing when an arch implements the
+          context tracking backend but doesn't yet fullfill all the
+          requirements to make the full dynticks feature working.
+          Without the full dynticks, there is no way to test the support
+          for context tracking and the subsystems that rely on it: RCU
+          userspace extended quiescent state and tickless cputime
+          accounting. This option copes with the absence of the full
+          dynticks subsystem by forcing the context tracking on all
+          CPUs in the system.
+
+          Say Y only if you're working on the developpement of an
+          architecture backend for the context tracking.
+
+          Say N otherwise, this option brings an overhead that you
+          don't want in production.
+
 
 config RCU_FANOUT
         int "Tree-based hierarchical RCU fanout value"