With PREEMPTION being always-on, some configurations might prefer the stronger forward-progress guarantees provided by PREEMPT_RCU=n as compared to PREEMPT_RCU=y. So, select PREEMPT_RCU=n for PREEMPT_VOLUNTARY and PREEMPT_NONE and enabling PREEMPT_RCU=y for PREEMPT or PREEMPT_RT. Note that the preemption model can be changed at runtime (modulo configurations with ARCH_NO_PREEMPT), but the RCU configuration is statically compiled. Cc: Simon Horman <horms@xxxxxxxxxxxx> Cc: Julian Anastasov <ja@xxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx> --- CC-note: Paul had flagged some code that might be impacted with the proposed RCU changes: 1. My guess is that the IPVS_EST_TICK_CHAINS heuristic remains unchanged, but I must defer to the include/net/ip_vs.h people. 2. I need to check with the BPF folks on the BPF verifier's definition of BTF_ID(func, rcu_read_unlock_strict). 3. I must defer to others on the mm/pgtable-generic.c file's #ifdef that depends on CONFIG_PREEMPT_RCU. Detailed here: https://lore.kernel.org/lkml/a375674b-de27-4965-a4bf-e0679229e28e@paulmck-laptop/ --- include/linux/rcutree.h | 2 +- kernel/rcu/Kconfig | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 126f6b418f6a..75aaa6294421 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -104,7 +104,7 @@ extern int rcu_scheduler_active; void rcu_end_inkernel_boot(void); bool rcu_inkernel_boot_has_ended(void); bool rcu_is_watching(void); -#ifndef CONFIG_PREEMPTION +#ifndef CONFIG_PREEMPT void rcu_all_qs(void); #endif diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index bdd7eadb33d8..a808cb29ab7c 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 select TREE_RCU help This option selects the RCU implementation that is @@ -31,7 +31,7 @@ config PREEMPT_RCU config TINY_RCU bool - default y if !PREEMPTION && !SMP + default y if !PREEMPT && !SMP help This option selects the RCU implementation that is designed for UP systems from which real-time response -- 2.31.1
