rcu: Remove single-rcu_node optimization in rcu_start_gp() (f38bd102) · Commits · 戴 / test

The grace-period initialization sequence in rcu_start_gp() has a special case for systems where the rcu_node tree is a single rcu_node structure. This made sense some years ago when systems were smaller and up to 64 CPUs could share a single rcu_node structure, but now that large systems are common and a given leaf rcu_node structure can support only 16 CPUs (due to lock contention on the rcu_node's ->lock field), this optimization is almost never taken. And even the small mobile platforms that might make use of it might rather have the kernel text reduction. Therefore, this commit removes the check for single-rcu_node trees. Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by:

Josh Triplett <josh@joshtriplett.org>

kernel/rcutree.c

+0 −18

Original line number	Diff line number	Diff line
		@@ -984,26 +984,8 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
		rsp->fqs_state = RCU_GP_INIT; /* Hold off force_quiescent_state. */
		rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
		record_gp_stall_check_time(rsp);

		/* Special-case the common single-level case. */
		if (NUM_RCU_NODES == 1) {
		rcu_preempt_check_blocked_tasks(rnp);
		rnp->qsmask = rnp->qsmaskinit;
		rnp->gpnum = rsp->gpnum;
		rnp->completed = rsp->completed;
		rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state OK */
		rcu_start_gp_per_cpu(rsp, rnp, rdp);
		rcu_preempt_boost_start_gp(rnp);
		trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
		rnp->level, rnp->grplo,
		rnp->grphi, rnp->qsmask);
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return;
		}

		raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */


		/* Exclude any concurrent CPU-hotplug operations. */
		raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */

Admin message