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[rcu,08/14] percpu-refcount: Use call_rcu_flush() for atomic switch

Message ID 20221019225144.2500095-8-paulmck@kernel.org
State New
Headers
Series Lazy call_rcu() updates for v6.2 |

Commit Message

Paul E. McKenney Oct. 19, 2022, 10:51 p.m. UTC 
  From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

call_rcu() changes to save power will slow down the percpu refcounter's
"per-CPU to atomic switch" path. The primitive uses RCU when switching to
atomic mode. The enqueued async callback wakes up waiters waiting in the
percpu_ref_switch_waitq. Due to this, per-CPU refcount users will slow down,
such as blk_pre_runtime_suspend().

Use the call_rcu_flush() API instead which reverts to the old behavior.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 lib/percpu-refcount.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
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Patch

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index e5c5315da2741..65c58a029297d 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -230,7 +230,8 @@  static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,
 		percpu_ref_noop_confirm_switch;
 
 	percpu_ref_get(ref);	/* put after confirmation */
-	call_rcu(&ref->data->rcu, percpu_ref_switch_to_atomic_rcu);
+	call_rcu_flush(&ref->data->rcu,
+		       percpu_ref_switch_to_atomic_rcu);
 }
 
 static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)