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Commit 7f5d42d0 authored Jan 31, 2018 by Paul E. McKenney

rcu: Trace expedited GP delays due to transitioning CPUs



If a CPU is transitioning to or from offline state, an expedited
grace period may undergo a timed wait.  This timed wait can unduly
delay grace periods, so this commit adds a trace statement to make
it visible.

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

parent 9a414201

include/trace/events/rcu.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -181,6 +181,7 @@ TRACE_EVENT(rcu_grace_period_init,
		* "start": Started a real expedited grace period.
		* "reset": Started resetting the tree
		* "select": Started selecting the CPUs to wait on.
		* "selectofl": Selected CPU partially offline.
		* "startwait": Started waiting on selected CPUs.
		* "end": Ended a real expedited grace period.
		* "endwake": Woke piggybackers up.

kernel/rcu/tree_exp.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -32,7 +32,7 @@ static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
		* Return then value that expedited-grace-period counter will have
		* at the end of the current grace period.
		*/
		static unsigned long rcu_exp_gp_seq_endval(struct rcu_state *rsp)
		static __maybe_unused unsigned long rcu_exp_gp_seq_endval(struct rcu_state *rsp)
		{
		return rcu_seq_endval(&rsp->expedited_sequence);
		}
		@@ -428,6 +428,7 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
		(rnp->expmask & mask)) {
		/* Online, so delay for a bit and try again. */
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("selectofl"));
		schedule_timeout_uninterruptible(1);
		goto retry_ipi;
		}