[PATCH 22/27] nohz: Don't turn off the tick if rcu needs it
If RCU is waiting for the current CPU to complete a grace period, don't turn off the tick. Unlike dynctik-idle, we are not necessarily going to enter into rcu extended quiescent state, so we may need to keep the tick to note current CPU's quiescent states. [added build fix from Zen Lin] CHECKME: OTOH we don't want to handle a locally started grace period, this should be offloaded for rcu_nocb CPUs. What we want is to be kicked if we stay dynticks in the kernel for too long (ie: to report a quiescent state). rcu_pending() is perhaps an overkill just for that. Signed-off-by: Frederic Weisbecker Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Chris Metcalf Cc: Christoph Lameter Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Paul E. McKenney Cc: Paul Gortmaker Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Signed-off-by: Steven Rostedt --- include/linux/rcupdate.h |1 + kernel/rcutree.c |3 +-- kernel/time/tick-sched.c |3 +++ 3 files changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 829312e..2ebadac 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -211,6 +211,7 @@ static inline int rcu_preempt_depth(void) extern void rcu_sched_qs(int cpu); extern void rcu_bh_qs(int cpu); extern void rcu_check_callbacks(int cpu, int user); +extern int rcu_pending(int cpu); struct notifier_block; extern void rcu_idle_enter(void); extern void rcu_idle_exit(void); diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e9e0ffa..6ba3e02 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -232,7 +232,6 @@ module_param(jiffies_till_next_fqs, ulong, 0644); static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); static void force_quiescent_state(struct rcu_state *rsp); -static int rcu_pending(int cpu); /* * Return the number of RCU-sched batches processed thus far for debug & stats. @@ -2521,7 +2520,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) * by the current CPU, returning 1 if so. This function is part of the * RCU implementation; it is -not- an exported member of the RCU API. */ -static int rcu_pending(int cpu) +int rcu_pending(int cpu) { struct rcu_state *rsp; diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 78e5341..04504c4 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -596,6 +596,9 @@ static bool can_stop_full_tick(int cpu) if (!rcu_is_nocb_cpu(cpu)) return false; + if (rcu_pending(cpu)) + return false; + return true; } #endif -- 1.7.5.4 -- 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/
[PATCH 22/27] nohz: Don't turn off the tick if rcu needs it
If RCU is waiting for the current CPU to complete a grace period, don't turn off the tick. Unlike dynctik-idle, we are not necessarily going to enter into rcu extended quiescent state, so we may need to keep the tick to note current CPU's quiescent states. [added build fix from Zen Lin] CHECKME: OTOH we don't want to handle a locally started grace period, this should be offloaded for rcu_nocb CPUs. What we want is to be kicked if we stay dynticks in the kernel for too long (ie: to report a quiescent state). rcu_pending() is perhaps an overkill just for that. Signed-off-by: Frederic Weisbecker fweis...@gmail.com Cc: Alessio Igor Bogani abog...@kernel.org Cc: Andrew Morton a...@linux-foundation.org Cc: Chris Metcalf cmetc...@tilera.com Cc: Christoph Lameter c...@linux.com Cc: Geoff Levand ge...@infradead.org Cc: Gilad Ben Yossef gi...@benyossef.com Cc: Hakan Akkan hakanak...@gmail.com Cc: Ingo Molnar mi...@kernel.org Cc: Paul E. McKenney paul...@linux.vnet.ibm.com Cc: Paul Gortmaker paul.gortma...@windriver.com Cc: Peter Zijlstra pet...@infradead.org Cc: Steven Rostedt rost...@goodmis.org Cc: Thomas Gleixner t...@linutronix.de Signed-off-by: Steven Rostedt rost...@goodmis.org --- include/linux/rcupdate.h |1 + kernel/rcutree.c |3 +-- kernel/time/tick-sched.c |3 +++ 3 files changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 829312e..2ebadac 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -211,6 +211,7 @@ static inline int rcu_preempt_depth(void) extern void rcu_sched_qs(int cpu); extern void rcu_bh_qs(int cpu); extern void rcu_check_callbacks(int cpu, int user); +extern int rcu_pending(int cpu); struct notifier_block; extern void rcu_idle_enter(void); extern void rcu_idle_exit(void); diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e9e0ffa..6ba3e02 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -232,7 +232,6 @@ module_param(jiffies_till_next_fqs, ulong, 0644); static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); static void force_quiescent_state(struct rcu_state *rsp); -static int rcu_pending(int cpu); /* * Return the number of RCU-sched batches processed thus far for debug stats. @@ -2521,7 +2520,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) * by the current CPU, returning 1 if so. This function is part of the * RCU implementation; it is -not- an exported member of the RCU API. */ -static int rcu_pending(int cpu) +int rcu_pending(int cpu) { struct rcu_state *rsp; diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 78e5341..04504c4 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -596,6 +596,9 @@ static bool can_stop_full_tick(int cpu) if (!rcu_is_nocb_cpu(cpu)) return false; + if (rcu_pending(cpu)) + return false; + return true; } #endif -- 1.7.5.4 -- 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/