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    SubjectRe: [PATCH tip/core/rcu 10/23] rcu: Allow RCU quiescent-state forcing to be preempted
    On Thu, Aug 30, 2012 at 11:18:25AM -0700, Paul E. McKenney wrote:
    > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    >
    > RCU quiescent-state forcing is currently carried out without preemption
    > points, which can result in excessive latency spikes on large systems
    > (many hundreds or thousands of CPUs). This patch therefore inserts
    > a voluntary preemption point into force_qs_rnp(), which should greatly
    > reduce the magnitude of these spikes.
    >
    > 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 | 1 +
    > 1 files changed, 1 insertions(+), 0 deletions(-)
    >
    > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    > index 79c2c28..cce73ff 100644
    > --- a/kernel/rcutree.c
    > +++ b/kernel/rcutree.c
    > @@ -1784,6 +1784,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
    > struct rcu_node *rnp;
    >
    > rcu_for_each_leaf_node(rsp, rnp) {
    > + cond_resched();
    > mask = 0;
    > raw_spin_lock_irqsave(&rnp->lock, flags);
    > if (!rcu_gp_in_progress(rsp)) {
    > --
    > 1.7.8
    >


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