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SubjectRe: [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@sgi.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@sgi.com>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Tested-by: Dimitri Sivanich <sivanich@sgi.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.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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