rcu: Report expedited grace periods at context-switch time (ba1c64c2) · Commits · 戴 / test

This commit reduces the latency of expedited RCU grace periods by reporting a quiescent state for the CPU at context-switch time. In CONFIG_PREEMPT=y kernels, if the outgoing task is still within an RCU read-side critical section (and thus still blocking some grace period, perhaps including this expedited grace period), then that task will already have been placed on one of the leaf rcu_node structures' ->blkd_tasks list. Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree_plugin.h

+3 −2

Original line number	Diff line number	Diff line
		@@ -332,7 +332,7 @@ static void rcu_preempt_qs(void)
		static void rcu_preempt_note_context_switch(bool preempt)
		{
		struct task_struct *t = current;
		struct rcu_data *rdp;
		struct rcu_data *rdp = this_cpu_ptr(rcu_state_p->rda);
		struct rcu_node *rnp;

		lockdep_assert_irqs_disabled();
		@@ -341,7 +341,6 @@ static void rcu_preempt_note_context_switch(bool preempt)
		!t->rcu_read_unlock_special.b.blocked) {

		/* Possibly blocking in an RCU read-side critical section. */
		rdp = this_cpu_ptr(rcu_state_p->rda);
		rnp = rdp->mynode;
		raw_spin_lock_rcu_node(rnp);
		t->rcu_read_unlock_special.b.blocked = true;
		@@ -383,6 +382,8 @@ static void rcu_preempt_note_context_switch(bool preempt)
		* means that we continue to block the current grace period.
		*/
		rcu_preempt_qs();
		if (rdp->deferred_qs)
		rcu_report_exp_rdp(rcu_state_p, rdp, true);
		}

		/*

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