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nohz_full: Force RCU's grace-period kthreads onto timekeeping CPU

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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@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2013-06-21 17:10:40 -07:00
parent 0edd1b1784
commit eb75767be0
3 changed files with 22 additions and 1 deletions
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1
kernel/rcutree.c
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@ -1303,6 +1303,7 @@ 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. */

1
kernel/rcutree.h
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@ -560,6 +560,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
static bool is_sysidle_rcu_state(struct rcu_state *rsp);
static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
unsigned long maxj);
static void rcu_bind_gp_kthread(void);
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp);
#endif /* #ifndef RCU_TREE_NONCORE */

21
kernel/rcutree_plugin.h
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@ -2531,7 +2531,8 @@ 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); */
if (rcu_gp_in_progress(rdp->rsp))
WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
/* Pick up current idle and NMI-nesting counter and check. */
cur = atomic_read(&rdtp->dynticks_idle);
@ -2556,6 +2557,20 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp)
return rsp == rcu_sysidle_state;
}
/*
* 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
@ -2766,6 +2781,10 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp)
return false;
}
static void rcu_bind_gp_kthread(void)
{
}
static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
unsigned long maxj)
{