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[7/9] rcu: limit PREEMPT_RCU configurations

Message ID 20250116201327.3782963-7-paulmck@kernel.org (mailing list archive)
State Accepted
Commit ef153339b0b035e2207734c84a8141af37113ea3
Headers show
Series Lazy-preemption-related updates | expand

Commit Message

Paul E. McKenney Jan. 16, 2025, 8:13 p.m. UTC 
From: Ankur Arora <ankur.a.arora@oracle.com>

PREEMPT_LAZY can be enabled stand-alone or alongside PREEMPT_DYNAMIC
which allows for dynamic switching of preemption models.

The choice of PREEMPT_RCU or not, however, is fixed at compile time.

Given that PREEMPT_RCU makes some trade-offs to optimize for latency
as opposed to throughput, configurations with limited preemption
might prefer the stronger forward-progress guarantees of PREEMPT_RCU=n.

Accordingly, explicitly limit PREEMPT_RCU=y to the latency oriented
preemption models: PREEMPT, PREEMPT_RT, and the runtime configurable
model PREEMPT_DYNAMIC.

This means the throughput oriented models, PREEMPT_NONE,
PREEMPT_VOLUNTARY, and PREEMPT_LAZY will run with PREEMPT_RCU=n.

Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 582d461c9ab7d..80242957fa417 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -18,7 +18,7 @@  config TREE_RCU
 
 config PREEMPT_RCU
 	bool
-	default y if PREEMPTION
+	default y if (PREEMPT || PREEMPT_RT || PREEMPT_DYNAMIC)
 	select TREE_RCU
 	help
 	  This option selects the RCU implementation that is