linux-kernel - Re: [RFC PATCH 47/86] rcu: select PREEMPT

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Message-ID: <ed7c9c16-1f66-4c96-e532-ae74e52c270b@ssi.bg>
Date:   Wed, 8 Nov 2023 14:15:35 +0200 (EET)
From:   Julian Anastasov <ja@....bg>
To:     Ankur Arora <ankur.a.arora@...cle.com>
cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, torvalds@...ux-foundation.org,
        paulmck@...nel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
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        David.Laight@...LAB.COM, richard@....at, mjguzik@...il.com,
        Simon Horman <horms@...ge.net.au>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [RFC PATCH 47/86] rcu: select PREEMPT_RCU if PREEMPT


	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@...ge.net.au>
> Cc: Julian Anastasov <ja@....bg>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> 
> ---
> 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@....bg>