rcu: Settle config for userspace extended quiescent state

Create a new config option under the RCU menu that put
CPUs under RCU extended quiescent state (as in dynticks
idle mode) when they run in userspace. This require
some contribution from architectures to hook into kernel
and userspace boundaries.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/arch/Kconfig b/arch/Kconfig
index 8c3d957fa8e2f6b7794223791136c75d6a66b412..1c7c9beaa1933234a62da487cdf255d6a7e76cb5 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -274,4 +274,14 @@ config SECCOMP_FILTER
 
          See Documentation/prctl/seccomp_filter.txt for details.
 
+config HAVE_RCU_USER_QS
+       bool
+       help
+         Provide kernel entry/exit hooks necessary for userspace
+         RCU extended quiescent state. Syscalls need to be wrapped inside
+         rcu_user_exit()-rcu_user_enter() through the slow path using
+         TIF_NOHZ flag. Exceptions handlers must be wrapped as well. Irqs
+         are already protected inside rcu_irq_enter/rcu_irq_exit() but
+         preemption or signal handling on irq exit still need to be protected.
+
 source "kernel/gcov/Kconfig"

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 81d3d5c53c43a6d5e274d4119631f49989fba271..e4111171c0c7d453ee9fb3ec0a93025a0f65f99d 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -191,10 +191,18 @@ extern void rcu_idle_enter(void);
 extern void rcu_idle_exit(void);
 extern void rcu_irq_enter(void);
 extern void rcu_irq_exit(void);
+
+#ifdef CONFIG_RCU_USER_QS
 extern void rcu_user_enter(void);
 extern void rcu_user_exit(void);
 extern void rcu_user_enter_irq(void);
 extern void rcu_user_exit_irq(void);
+#else
+static inline void rcu_user_enter(void) { }
+static inline void rcu_user_exit(void) { }
+#endif /* CONFIG_RCU_USER_QS */
+
+
 extern void exit_rcu(void);
 
 /**

diff --git a/init/Kconfig b/init/Kconfig
index d07dcf9fc8a9a8f05a570298d106c29e28f7167f..3a4af8fc58553b079adf267f1dedc74c45f514c1 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -441,6 +441,16 @@ config PREEMPT_RCU
          This option enables preemptible-RCU code that is common between
          the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
 
+config RCU_USER_QS
+       bool "Consider userspace as in RCU extended quiescent state"
+       depends on HAVE_RCU_USER_QS && SMP
+       help
+         This option sets hooks on kernel / userspace boundaries and
+         puts RCU in extended quiescent state when the CPU runs in
+         userspace. It means that when a CPU runs in userspace, it is
+         excluded from the global RCU state machine and thus doesn't
+         to keep the timer tick on for RCU.
+
 config RCU_FANOUT
        int "Tree-based hierarchical RCU fanout value"
        range 2 64 if 64BIT

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 8fdea17af81d5bfdb158a1b9e10a07dbf9a969d1..e287c4a0d81c083c86df312f8c5c7fe305a511fe 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -424,6 +424,7 @@ void rcu_idle_enter(void)
 }
 EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
+#ifdef CONFIG_RCU_USER_QS
 /**
  * rcu_user_enter - inform RCU that we are resuming userspace.
  *
@@ -438,7 +439,6 @@ void rcu_user_enter(void)
 }
 EXPORT_SYMBOL_GPL(rcu_user_enter);
 
-
 /**
  * rcu_user_enter_irq - inform RCU that we are going to resume userspace
  * after the current irq returns.
@@ -459,6 +459,7 @@ void rcu_user_enter_irq(void)
        rdtp->dynticks_nesting = 1;
        local_irq_restore(flags);
 }
+#endif
 
 /**
  * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
@@ -562,6 +563,7 @@ void rcu_idle_exit(void)
 }
 EXPORT_SYMBOL_GPL(rcu_idle_exit);
 
+#ifdef CONFIG_RCU_USER_QS
 /**
  * rcu_user_exit - inform RCU that we are exiting userspace.
  *
@@ -595,6 +597,7 @@ void rcu_user_exit_irq(void)
        rdtp->dynticks_nesting += DYNTICK_TASK_EXIT_IDLE;
        local_irq_restore(flags);
 }
+#endif
 
 /**
  * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle