Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 22/24] nohz: Don't turn off the tick if rcu needs it | Date | Thu, 20 Dec 2012 19:33:09 +0100 |
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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 <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: Ingo Molnar <mingo@kernel.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Steven Rostedt <rostedt@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 2808e02..0c9281a 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -594,6 +594,9 @@ 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
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