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rcu: Make synchronize_rcu() fastpath update only boot-CPU counters

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Large systems can have hundreds of rcu_node structures, and updating
counters in each of them might slow down booting.  This commit therefore
updates only the counters in those rcu_node structures corresponding
to the boot CPU, up to and including the root rcu_node structure.

The counters for the remaining rcu_node structures are updated by the
rcu_scheduler_starting() function, which executes just before the first
non-boot kthread is spawned.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-08-05 15:42:25 -07:00
parent b3cdd0a79c
commit d761de8a7d
1 changed files with 16 additions and 2 deletions
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18
kernel/rcu/tree.c
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@ -3504,11 +3504,14 @@ void synchronize_rcu(void)
rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
// Update normal grace-period counters to record grace period.
// Update the normal grace-period counters to record
// this grace period, but only those used by the boot CPU.
// The rcu_scheduler_starting() will take care of the rest of
// these counters.
local_irq_save(flags);
WARN_ON_ONCE(num_online_cpus() > 1);
rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT);
rcu_for_each_node_breadth_first(rnp)
for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent)
rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
local_irq_restore(flags);
}
@ -4456,9 +4459,20 @@ early_initcall(rcu_spawn_gp_kthread);
*/
void rcu_scheduler_starting(void)
{
unsigned long flags;
struct rcu_node *rnp;
WARN_ON(num_online_cpus() != 1);
WARN_ON(nr_context_switches() > 0);
rcu_test_sync_prims();
// Fix up the ->gp_seq counters.
local_irq_save(flags);
rcu_for_each_node_breadth_first(rnp)
rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
local_irq_restore(flags);
// Switch out of early boot mode.
rcu_scheduler_active = RCU_SCHEDULER_INIT;
rcu_test_sync_prims();
}