Commit-ID: 1ce46ee597bc36fde6984e91aecc2d662a754199
Gitweb: http://git.kernel.org/tip/1ce46ee597bc36fde6984e91aecc2d662a754199
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Tue, 5 May 2015 23:04:22 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed, 27 May 2015 12:59:07 -0700
rcu: Conditionally compile RCU's eqs warnings
This commit applies some warning-omission micro-optimizations to RCU's
various extended-quiescent-state functions, which are on the kernel/user
hotpath for CONFIG_NO_HZ_FULL=y.
Reported-by: Rik van Riel <riel@xxxxxxxxxx>
Reported by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 23 +++++++++++++++--------
lib/Kconfig.debug | 11 +++++++++++
2 files changed, 26 insertions(+), 8 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0e9ce12..991fa5c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -620,7 +620,8 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
- if (!user && !is_idle_task(current)) {
+ if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+ !user && !is_idle_task(current)) {
struct task_struct *idle __maybe_unused =
idle_task(smp_processor_id());
@@ -639,7 +640,8 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
smp_mb__before_atomic(); /* See above. */
atomic_inc(&rdtp->dynticks);
smp_mb__after_atomic(); /* Force ordering with next sojourn. */
- WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+ atomic_read(&rdtp->dynticks) & 0x1);
rcu_dynticks_task_enter();
/*
@@ -665,7 +667,8 @@ static void rcu_eqs_enter(bool user)
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
- WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+ (oldval & DYNTICK_TASK_NEST_MASK) == 0);
if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
rdtp->dynticks_nesting = 0;
rcu_eqs_enter_common(oldval, user);
@@ -738,7 +741,8 @@ void rcu_irq_exit(void)
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting--;
- WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+ rdtp->dynticks_nesting < 0);
if (rdtp->dynticks_nesting)
trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
else
@@ -763,10 +767,12 @@ static void rcu_eqs_exit_common(long long oldval, int user)
atomic_inc(&rdtp->dynticks);
/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
smp_mb__after_atomic(); /* See above. */
- WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+ !(atomic_read(&rdtp->dynticks) & 0x1));
rcu_cleanup_after_idle();
trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
- if (!user && !is_idle_task(current)) {
+ if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+ !user && !is_idle_task(current)) {
struct task_struct *idle __maybe_unused =
idle_task(smp_processor_id());
@@ -790,7 +796,7 @@ static void rcu_eqs_exit(bool user)
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
- WARN_ON_ONCE(oldval < 0);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
if (oldval & DYNTICK_TASK_NEST_MASK) {
rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
} else {
@@ -863,7 +869,8 @@ void rcu_irq_enter(void)
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting++;
- WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+ rdtp->dynticks_nesting == 0);
if (oldval)
trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
else
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c4e1cf0..b908048 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1373,6 +1373,17 @@ config RCU_TRACE
Say Y here if you want to enable RCU tracing
Say N if you are unsure.
+config RCU_EQS_DEBUG
+ bool "Use this when adding any sort of NO_HZ support to your arch"
+ depends on DEBUG_KERNEL
+ help
+ This option provides consistency checks in RCU's handling of
+ NO_HZ. These checks have proven quite helpful in detecting
+ bugs in arch-specific NO_HZ code.
+
+ Say N here if you need ultimate kernel/user switch latencies
+ Say Y if you are unsure
+
endmenu # "RCU Debugging"
config DEBUG_BLOCK_EXT_DEVT
--
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