diff mbox series

[4/9] rcu: Register rcu-lazy shrinker only for CONFIG_RCU_LAZY=y kernels

Message ID 20230315194349.10798-4-joel@joelfernandes.org
State New
Headers
Series [1/9] rcu: Fix set/clear TICK_DEP_BIT_RCU_EXP bitmask race |

Commit Message

Joel Fernandes March 15, 2023, 7:43 p.m. UTC 
  From: Zqiang <qiang1.zhang@intel.com>

The lazy_rcu_shrink_count() shrinker function is registered even in
kernels built with CONFIG_RCU_LAZY=n, in which case this function
uselessly consumes cycles learning that no CPU has any lazy callbacks
queued.

This commit therefore registers this shrinker function only in the kernels
built with CONFIG_RCU_LAZY=y, where it might actually do something useful.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/rcu/tree_nocb.h | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Frederic Weisbecker March 15, 2023, 11:19 p.m. UTC | #1 
Le Wed, Mar 15, 2023 at 07:43:44PM +0000, Joel Fernandes (Google) a écrit :
> From: Zqiang <qiang1.zhang@intel.com>
> 
> The lazy_rcu_shrink_count() shrinker function is registered even in
> kernels built with CONFIG_RCU_LAZY=n, in which case this function
> uselessly consumes cycles learning that no CPU has any lazy callbacks
> queued.
> 
> This commit therefore registers this shrinker function only in the kernels
> built with CONFIG_RCU_LAZY=y, where it might actually do something useful.
> 
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Joel Fernandes March 16, 2023, 2:28 a.m. UTC | #2 
On Thu, Mar 16, 2023 at 12:19:19AM +0100, Frederic Weisbecker wrote:
> Le Wed, Mar 15, 2023 at 07:43:44PM +0000, Joel Fernandes (Google) a écrit :
> > From: Zqiang <qiang1.zhang@intel.com>
> > 
> > The lazy_rcu_shrink_count() shrinker function is registered even in
> > kernels built with CONFIG_RCU_LAZY=n, in which case this function
> > uselessly consumes cycles learning that no CPU has any lazy callbacks
> > queued.
> > 
> > This commit therefore registers this shrinker function only in the kernels
> > built with CONFIG_RCU_LAZY=y, where it might actually do something useful.
> > 
> > Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

Thanks!

 - Joel
diff mbox series

Patch

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 9e1c8caec5ce..f2280616f9d5 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1312,6 +1312,7 @@  int rcu_nocb_cpu_offload(int cpu)
 }
 EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
 
+#ifdef CONFIG_RCU_LAZY
 static unsigned long
 lazy_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
@@ -1360,6 +1361,7 @@  static struct shrinker lazy_rcu_shrinker = {
 	.batch = 0,
 	.seeks = DEFAULT_SEEKS,
 };
+#endif // #ifdef CONFIG_RCU_LAZY
 
 void __init rcu_init_nohz(void)
 {
@@ -1391,8 +1393,10 @@  void __init rcu_init_nohz(void)
 	if (!rcu_state.nocb_is_setup)
 		return;
 
+#ifdef CONFIG_RCU_LAZY
 	if (register_shrinker(&lazy_rcu_shrinker, "rcu-lazy"))
 		pr_err("Failed to register lazy_rcu shrinker!\n");
+#endif // #ifdef CONFIG_RCU_LAZY
 
 	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
 		pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");