From: Paul E. McKenney Date: Fri, 13 Nov 2009 06:35:03 +0000 (-0800) Subject: rcu: Accelerate callback processing on CPUs not detecting GP end X-Git-Tag: firefly_0821_release~9833^2~3985^2~10 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=b32e9eb6ad29572b4451847d0e8227c9be2b6d69;p=firefly-linux-kernel-4.4.55.git rcu: Accelerate callback processing on CPUs not detecting GP end An earlier fix for a race resulted in a situation where the CPUs other than the CPU that detected the end of the grace period would not process their callbacks until the next grace period started. This means that these other CPUs would unnecessarily demand that an extra grace period be started. This patch eliminates this extra grace period and speeds callback processing by propagating rsp->completed to the rcu_node structures in the case where the CPU detecting the end of the grace period sees no reason to start a new grace period. Signed-off-by: Paul E. McKenney Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1258094104417-git-send-email-> Signed-off-by: Ingo Molnar --- diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d8024192c73b..b4efb9e36680 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -676,7 +676,23 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) struct rcu_node *rnp = rcu_get_root(rsp); if (!cpu_needs_another_gp(rsp, rdp)) { - spin_unlock_irqrestore(&rnp->lock, flags); + if (rnp->completed == rsp->completed) { + spin_unlock_irqrestore(&rnp->lock, flags); + return; + } + spin_unlock(&rnp->lock); /* irqs remain disabled. */ + + /* + * Propagate new ->completed value to rcu_node structures + * so that other CPUs don't have to wait until the start + * of the next grace period to process their callbacks. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + spin_lock(&rnp->lock); /* irqs already disabled. */ + rnp->completed = rsp->completed; + spin_unlock(&rnp->lock); /* irqs remain disabled. */ + } + local_irq_restore(flags); return; }