Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney:

  * Remove restrictions on no-CBs CPUs, make RCU_FAST_NO_HZ
    take advantage of numbered callbacks, do additional callback
    accelerations based on numbered callbacks.  Posted to LKML
    at https://lkml.org/lkml/2013/3/18/960.

  * RCU documentation updates.  Posted to LKML at
    https://lkml.org/lkml/2013/3/18/570.

  * Miscellaneous fixes.  Posted to LKML at
    https://lkml.org/lkml/2013/3/18/594.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 58 insertions, 15 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 5341d7232c3a..71bb9e73011a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -578,13 +578,16 @@ config RCU_FAST_NO_HZ
         depends on NO_HZ && SMP
         default n
         help
-          This option causes RCU to attempt to accelerate grace periods in
-          order to allow CPUs to enter dynticks-idle state more quickly.
-          On the other hand, this option increases the overhead of the
-          dynticks-idle checking, thus degrading scheduling latency.
+          This option permits CPUs to enter dynticks-idle state even if
+          they have RCU callbacks queued, and prevents RCU from waking
+          these CPUs up more than roughly once every four jiffies (by
+          default, you can adjust this using the rcutree.rcu_idle_gp_delay
+          parameter), thus improving energy efficiency.  On the other
+          hand, this option increases the duration of RCU grace periods,
+          for example, slowing down synchronize_rcu().
 
-          Say Y if energy efficiency is critically important, and you don't
-                care about real-time response.
+          Say Y if energy efficiency is critically important, and you
+                don't care about increased grace-period durations.
 
           Say N if you are unsure.
 
@@ -651,7 +654,7 @@ config RCU_BOOST_DELAY
           Accept the default if unsure.
 
 config RCU_NOCB_CPU
-        bool "Offload RCU callback processing from boot-selected CPUs"
+        bool "Offload RCU callback processing from boot-selected CPUs (EXPERIMENTAL"
         depends on TREE_RCU || TREE_PREEMPT_RCU
         default n
         help
@@ -662,16 +665,56 @@ config RCU_NOCB_CPU
 
           This option offloads callback invocation from the set of
           CPUs specified at boot time by the rcu_nocbs parameter.
-          For each such CPU, a kthread ("rcuoN") will be created to
-          invoke callbacks, where the "N" is the CPU being offloaded.
-          Nothing prevents this kthread from running on the specified
-          CPUs, but (1) the kthreads may be preempted between each
-          callback, and (2) affinity or cgroups can be used to force
-          the kthreads to run on whatever set of CPUs is desired.
-
-          Say Y here if you want reduced OS jitter on selected CPUs.
+          For each such CPU, a kthread ("rcuox/N") will be created to
+          invoke callbacks, where the "N" is the CPU being offloaded,
+          and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
+          "s" for RCU-sched.  Nothing prevents this kthread from running
+          on the specified CPUs, but (1) the kthreads may be preempted
+          between each callback, and (2) affinity or cgroups can be used
+          to force the kthreads to run on whatever set of CPUs is desired.
+
+          Say Y here if you want to help to debug reduced OS jitter.
           Say N here if you are unsure.
 
+choice
+        prompt "Build-forced no-CBs CPUs"
+        default RCU_NOCB_CPU_NONE
+        help
+          This option allows no-CBs CPUs to be specified at build time.
+          Additional no-CBs CPUs may be specified by the rcu_nocbs=
+          boot parameter.
+
+config RCU_NOCB_CPU_NONE
+        bool "No build_forced no-CBs CPUs"
+        depends on RCU_NOCB_CPU
+        help
+          This option does not force any of the CPUs to be no-CBs CPUs.
+          Only CPUs designated by the rcu_nocbs= boot parameter will be
+          no-CBs CPUs.
+
+config RCU_NOCB_CPU_ZERO
+        bool "CPU 0 is a build_forced no-CBs CPU"
+        depends on RCU_NOCB_CPU
+        help
+          This option forces CPU 0 to be a no-CBs CPU.  Additional CPUs
+          may be designated as no-CBs CPUs using the rcu_nocbs= boot
+          parameter will be no-CBs CPUs.
+
+          Select this if CPU 0 needs to be a no-CBs CPU for real-time
+          or energy-efficiency reasons.
+
+config RCU_NOCB_CPU_ALL
+        bool "All CPUs are build_forced no-CBs CPUs"
+        depends on RCU_NOCB_CPU
+        help
+          This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
+          boot parameter will be ignored.
+
+          Select this if all CPUs need to be no-CBs CPUs for real-time
+          or energy-efficiency reasons.
+
+endchoice
+
 endmenu # "RCU Subsystem"
 
 config IKCONFIG