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Message-Id: <1372450222-19420-7-git-send-email-paulmck@linux.vnet.ibm.com>
Date: Fri, 28 Jun 2013 13:10:22 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
sbw@....edu, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC nohz_full v2 7/7] nohz_full: Force RCU's grace-period kthreads onto timekeeping CPU
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Because RCU's quiescent-state-forcing mechanism is used to drive the
full-system-idle state machine, and because this mechanism is executed
by RCU's grace-period kthreads, this commit forces these kthreads to
run on the timekeeping CPU (tick_do_timer_cpu). To do otherwise would
mean that the RCU grace-period kthreads would force the system into
non-idle state every time they drove the state machine, which would
be just a bit on the futile side.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
---
kernel/rcutree.c | 1 +
kernel/rcutree.h | 1 +
kernel/rcutree_plugin.h | 20 +++++++++++++++++++-
3 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 06cfd75..ad9a5ec 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1286,6 +1286,7 @@ static int rcu_gp_init(struct rcu_state *rsp)
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root(rsp);
+ rcu_bind_gp_kthread();
raw_spin_lock_irq(&rnp->lock);
rsp->gp_flags = 0; /* Clear all flags: New grace period. */
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 7326a3c..1602c21 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -558,6 +558,7 @@ static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq);
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
unsigned long *maxj);
static bool is_sysidle_rcu_state(struct rcu_state *rsp);
+static void rcu_bind_gp_kthread(void);
static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
unsigned long maxj);
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 9b60df5..4478cfd 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2543,7 +2543,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
if (!*isidle || rdp->rsp != rcu_sysidle_state ||
cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
return;
- /* WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); */
+ WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
/*
* Pick up current idle and NMI-nesting counters, check. We check
@@ -2577,6 +2577,20 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp)
}
/*
+ * Bind the grace-period kthread for the sysidle flavor of RCU to the
+ * timekeeping CPU.
+ */
+static void rcu_bind_gp_kthread(void)
+{
+ int cpu = ACCESS_ONCE(tick_do_timer_cpu);
+
+ if (cpu < 0 || cpu >= nr_cpu_ids)
+ return;
+ if (raw_smp_processor_id() != cpu)
+ set_cpus_allowed_ptr(current, cpumask_of(cpu));
+}
+
+/*
* Return a delay in jiffies based on the number of CPUs, rcu_node
* leaf fanout, and jiffies tick rate. The idea is to allow larger
* systems more time to transition to full-idle state in order to
@@ -2744,6 +2758,10 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp)
return false;
}
+static void rcu_bind_gp_kthread(void)
+{
+}
+
static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
unsigned long maxj)
{
--
1.8.1.5
--
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