linux-kernel - Re: [PATCH tip/core/rcu 08/23] rcu: Segregate rcu

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Message-ID: <20120902025100.GA6786@leaf>
Date:	Sat, 1 Sep 2012 19:51:00 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	Dimitri Sivanich <sivanich@....com>
Subject: Re: [PATCH tip/core/rcu 08/23] rcu: Segregate rcu_state fields to
 improve cache locality

On Thu, Aug 30, 2012 at 11:18:23AM -0700, Paul E. McKenney wrote:
> From: Dimitri Sivanich <sivanich@....com>
> 
> The fields in the rcu_state structure that are protected by the
> root rcu_node structure's ->lock can share a cache line with the
> fields protected by ->onofflock.  This can result in excessive
> memory contention on large systems, so this commit applies
> ____cacheline_internodealigned_in_smp to the ->onofflock field in
> order to segregate them.
> 
> Signed-off-by: Dimitri Sivanich <sivanich@....com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Tested-by: Dimitri Sivanich <sivanich@....com>

Reviewed-by: Josh Triplett <josh@...htriplett.org>

>  kernel/rcutree.h |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/rcutree.h b/kernel/rcutree.h
> index effb273..5d92b80 100644
> --- a/kernel/rcutree.h
> +++ b/kernel/rcutree.h
> @@ -394,7 +394,8 @@ struct rcu_state {
>  
>  	/* End of fields guarded by root rcu_node's lock. */
>  
> -	raw_spinlock_t onofflock;		/* exclude on/offline and */
> +	raw_spinlock_t onofflock ____cacheline_internodealigned_in_smp;
> +						/* exclude on/offline and */
>  						/*  starting new GP. */
>  	struct rcu_head *orphan_nxtlist;	/* Orphaned callbacks that */
>  						/*  need a grace period. */
> -- 
> 1.7.8
> 
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