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rcu: Tighten up affinity and check for sysidle

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If the RCU grace-period kthread invoking rcu_sysidle_check_cpu()
happens to be running on the tick_do_timer_cpu initially,
then rcu_bind_gp_kthread() won't bind it.  This kthread might
then migrate before invoking rcu_gp_fqs(), which will trigger the
WARN_ON_ONCE() in rcu_sysidle_check_cpu().  This commit therefore makes
rcu_bind_gp_kthread() do the binding even if the kthread is currently
on the same CPU.  Because this incurs added overhead, this commit also
causes each RCU grace-period kthread to invoke rcu_bind_gp_kthread()
once at boot rather than at the beginning of each grace period.
And as long as rcu_bind_gp_kthread() is being modified, this commit
eliminates its #ifdef.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2015-02-24 11:05:36 -08:00
parent 675da67f24
commit 5871968d53
2 changed files with 7 additions and 7 deletions
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2
kernel/rcu/tree.c
View file

@ -1707,7 +1707,6 @@ static int rcu_gp_init(struct rcu_state *rsp)
struct rcu_node *rnp = rcu_get_root(rsp);
ACCESS_ONCE(rsp->gp_activity) = jiffies;
rcu_bind_gp_kthread();
raw_spin_lock_irq(&rnp->lock);
smp_mb__after_unlock_lock();
if (!ACCESS_ONCE(rsp->gp_flags)) {
@ -1895,6 +1894,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
struct rcu_state *rsp = arg;
struct rcu_node *rnp = rcu_get_root(rsp);
rcu_bind_gp_kthread();
for (;;) {
/* Handle grace-period start. */

12
kernel/rcu/tree_plugin.h
View file

@ -2763,7 +2763,8 @@ static void rcu_sysidle_exit(int irq)
/*
* Check to see if the current CPU is idle. Note that usermode execution
* does not count as idle. The caller must have disabled interrupts.
* does not count as idle. The caller must have disabled interrupts,
* and must be running on tick_do_timer_cpu.
*/
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
unsigned long *maxj)
@ -2784,8 +2785,8 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
if (!*isidle || rdp->rsp != rcu_state_p ||
cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
return;
if (rcu_gp_in_progress(rdp->rsp))
WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
/* Verify affinity of current kthread. */
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);
@ -3068,11 +3069,10 @@ static void rcu_bind_gp_kthread(void)
return;
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
cpu = tick_do_timer_cpu;
if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
if (cpu >= 0 && cpu < nr_cpu_ids)
set_cpus_allowed_ptr(current, cpumask_of(cpu));
#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
if (!is_housekeeping_cpu(raw_smp_processor_id()))
housekeeping_affine(current);
housekeeping_affine(current);
#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
}