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rcu: Trace expedited GP delays due to transitioning CPUs

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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>
This commit is contained in:
Paul E. McKenney 2018-01-31 19:40:22 -08:00
parent 9a414201ae
commit 7f5d42d051
2 changed files with 3 additions and 1 deletions
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1
include/trace/events/rcu.h
View File

@ -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.

3
kernel/rcu/tree_exp.h
View File

@ -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 @@ retry_ipi:
(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;
}