Re: [RFC PATCH 47/86] rcu: select PREEMPT_RCU if PREEMPT

[Julian Anastasov]

	Hello,

On Tue, 7 Nov 2023, Ankur Arora wrote:

> 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.

	Yes, IPVS_EST_TICK_CHAINS depends on the rcu_read_unlock()
and rcu_read_lock() calls in cond_resched_rcu(), so just removing
the cond_resched() call there is ok for us. Same for the other
cond_resched() calls in ipvs/

Regards

--
Julian Anastasov <ja@xxxxxx>