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SubjectRe: [PATCH tip/core/rcu 04/23] rcu: Allow RCU grace-period cleanup to be preempted
On Thu, Aug 30, 2012 at 11:18:19AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>
> RCU grace-period cleanup is currently carried out with interrupts
> disabled, which can result in excessive latency spikes on large systems
> (many hundreds or thousands of CPUs). This patch therefore makes the
> RCU grace-period cleanup be preemptible, including voluntary preemption
> points, which should eliminate those latency spikes. Similar spikes from
> forcing of quiescent states will be dealt with similarly by later patches.
>
> Reported-by: Mike Galbraith <mgalbraith@suse.de>
> Reported-by: Dimitri Sivanich <sivanich@sgi.com>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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

> kernel/rcutree.c | 11 +++++------
> 1 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 9fad21c..300aba6 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1170,7 +1170,7 @@ static int rcu_gp_kthread(void *arg)
> * completed.
> */
> if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
> - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
>
> /*
> * Propagate new ->completed value to rcu_node
> @@ -1179,14 +1179,13 @@ static int rcu_gp_kthread(void *arg)
> * to process their callbacks.
> */
> rcu_for_each_node_breadth_first(rsp, rnp) {
> - /* irqs already disabled. */
> - raw_spin_lock(&rnp->lock);
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> rnp->completed = rsp->gpnum;
> - /* irqs remain disabled. */
> - raw_spin_unlock(&rnp->lock);
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> + cond_resched();
> }
> rnp = rcu_get_root(rsp);
> - raw_spin_lock(&rnp->lock); /* irqs already disabled. */
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> }
>
> rsp->completed = rsp->gpnum; /* Declare grace period done. */
> --
> 1.7.8
>


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