From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
People with low-latency kernel-intensive workloads object to the
extra test of a per-CPU variable added to cond_resched(). This commit
therefore adds a Kconfig variable RCU_COND_RESCHED_QS that enables this
extra test. Therefore, people who would like large systems to operate
reliably can enable this Kconfig variable, while people with low-latency
kernel-intensive workloads can leave it disabled. People setting defaults
for Linux distributions should choose wisely. ;-)
Suggested-by: Christoph Lameter <c...@gentwo.org>
Suggested-by: Josh Triplett <j...@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Josh Triplett <j...@joshtriplett.org>
Cc: Andi Kleen <a...@linux.intel.com>
Cc: Christoph Lameter <c...@gentwo.org>
Cc: Mike Galbraith <umgwanakikb...@gmail.com>
Cc: Eric Dumazet <eric.duma...@gmail.com>
---
include/linux/rcutree.h | 15 +++++++++++++--
init/Kconfig | 26 ++++++++++++++++++++++++++
2 files changed, 39 insertions(+), 2 deletions(-)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index ca7d34027935..69ccd4163de2 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -56,12 +56,23 @@ static inline bool rcu_should_resched(void)
}
/* Report quiescent states to RCU if it is time to do so. */
-static inline void rcu_cond_resched(void)
+static inline void __rcu_cond_resched(void)
{
if (unlikely(rcu_should_resched()))
rcu_resched();
}
+/*
+ * Report quiescent states to RCU in kernels that are not configured
+ * for low-latency kernel-intensive workloads.
+ */
+static inline void rcu_cond_resched(void)
+{
+#ifdef CONFIG_RCU_COND_RESCHED_QS
+ __rcu_cond_resched();
+#endif /* #ifdef CONFIG_RCU_COND_RESCHED_QS */
+}
+
/**
* cond_resched_rcu_qs - Report potential quiescent states to RCU
*
@@ -71,7 +82,7 @@ static inline void rcu_cond_resched(void)
*/
#define cond_resched_rcu_qs() \
do { \
- rcu_cond_resched(); \
+ __rcu_cond_resched(); \
cond_resched(); \
} while (0)
diff --git a/init/Kconfig b/init/Kconfig
index 9d76b99af1b9..6457a7f1f0be 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -781,6 +781,32 @@ config RCU_NOCB_CPU_ALL
endchoice
+config RCU_COND_RESCHED_QS
+ bool "Use cond_resched() calls as RCU quiescent states"
+ depends on TREE_RCU || TREE_PREEMPT_RCU
+ default n
+ help
+ Use this option to allow RCU grace periods to make progress
+ on large systems that can execute for extended time periods
+ in the kernel. Workloads that contain processes with large
+ numbers of open files, systems with large quantities of
+ memory, workloads that do mm-related system calls on large
+ regions, and systems with large numbers of mass-storage
+ devices are particularly prone to this behavior. Without
+ this option set, RCU CPU stall warnings or even OOMs can
+ result.
+
+ This option causes cond_resched() to check to see if the
+ current RCU grace period has been waiting for too long for
+ this CPU, and to emulate a zero-duration dyntick-idle
+ period if so. RCU's grace-period kthreads will then note
+ this dyntick-idle period and report a quiescent state to
+ the RCU core on this CPU's behalf, thus avoiding both RCU
+ CPU stall warnings and OOMs.
+
+ Say Y here for reliable operation on large systems.
+ Say N here for kernel-intensive low-latency workloads.
+
endmenu # "RCU Subsystem"
config IKCONFIG
--
1.8.1.5
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
