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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-08-14 16:24:26 -0700 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-09-23 09:18:13 -0700 |
commit | 9261dd0da6c6432f08670719069449c6efe4f7a9 (patch) | |
tree | b8c95dd0e4751e3069e9263d6f46b86251d5dc35 | |
parent | bb311eccbdab974639263060b8452bf304af0b0c (diff) | |
download | op-kernel-dev-9261dd0da6c6432f08670719069449c6efe4f7a9.zip op-kernel-dev-9261dd0da6c6432f08670719069449c6efe4f7a9.tar.gz |
rcu: Add tracing for rcuo no-CBs CPU wakeup handshake
Lost wakeups from call_rcu() to the rcuo kthreads can result in hangs
that are difficult to diagnose. This commit therefore adds tracing to
help pin down the cause of these hangs.
Reported-by: Clark Williams <williams@redhat.com>
Reported-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Add const per kbuild test robot's advice. ]
-rw-r--r-- | include/trace/events/rcu.h | 37 | ||||
-rw-r--r-- | kernel/rcutree_plugin.h | 14 |
2 files changed, 50 insertions, 1 deletions
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index 98466c6..4301cd9 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -172,6 +172,42 @@ TRACE_EVENT(rcu_grace_period_init, ); /* + * Tracepoint for RCU no-CBs CPU callback handoffs. This event is intended + * to assist debugging of these handoffs. + * + * The first argument is the name of the RCU flavor, and the second is + * the number of the offloaded CPU are extracted. The third and final + * argument is a string as follows: + * + * "WakeEmpty": Wake rcuo kthread, first CB to empty list. + * "WakeOvf": Wake rcuo kthread, CB list is huge. + * "WakeNot": Don't wake rcuo kthread. + * "WakeNotPoll": Don't wake rcuo kthread because it is polling. + * "WokeEmpty": rcuo kthread woke to find empty list. + * "WokeNonEmpty": rcuo kthread woke to find non-empty list. + */ +TRACE_EVENT(rcu_nocb_wake, + + TP_PROTO(const char *rcuname, int cpu, const char *reason), + + TP_ARGS(rcuname, cpu, reason), + + TP_STRUCT__entry( + __field(const char *, rcuname) + __field(int, cpu) + __field(const char *, reason) + ), + + TP_fast_assign( + __entry->rcuname = rcuname; + __entry->cpu = cpu; + __entry->reason = reason; + ), + + TP_printk("%s %d %s", __entry->rcuname, __entry->cpu, __entry->reason) +); + +/* * Tracepoint for tasks blocking within preemptible-RCU read-side * critical sections. Track the type of RCU (which one day might * include SRCU), the grace-period number that the task is blocking @@ -667,6 +703,7 @@ TRACE_EVENT(rcu_barrier, #define trace_rcu_future_grace_period(rcuname, gpnum, completed, c, \ level, grplo, grphi, event) \ do { } while (0) +#define trace_rcu_nocb_wake(rcuname, cpu, reason) do { } while (0) #define trace_rcu_preempt_task(rcuname, pid, gpnum) do { } while (0) #define trace_rcu_unlock_preempted_task(rcuname, gpnum, pid) do { } while (0) #define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, \ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 130c97b..f4ed24b 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2108,15 +2108,22 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, /* If we are not being polled and there is a kthread, awaken it ... */ t = ACCESS_ONCE(rdp->nocb_kthread); - if (rcu_nocb_poll | !t) + if (rcu_nocb_poll | !t) { + trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, + TPS("WakeNotPoll")); return; + } len = atomic_long_read(&rdp->nocb_q_count); if (old_rhpp == &rdp->nocb_head) { wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */ rdp->qlen_last_fqs_check = 0; + trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeEmpty")); } else if (len > rdp->qlen_last_fqs_check + qhimark) { wake_up_process(t); /* ... or if many callbacks queued. */ rdp->qlen_last_fqs_check = LONG_MAX / 2; + trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf")); + } else { + trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); } return; } @@ -2233,10 +2240,15 @@ static int rcu_nocb_kthread(void *arg) wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head); list = ACCESS_ONCE(rdp->nocb_head); if (!list) { + if (!rcu_nocb_poll) + trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, + TPS("WokeEmpty")); schedule_timeout_interruptible(1); flush_signals(current); continue; } + trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, + TPS("WokeNonEmpty")); /* * Extract queued callbacks, update counts, and wait |