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Message-ID: <20200618235117.GA40119@google.com>
Date: Thu, 18 Jun 2020 19:51:17 -0400
From: Joel Fernandes <joel@...lfernandes.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
Ingo Molnar <mingo@...hat.com>,
Josh Triplett <josh@...htriplett.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Marco Elver <elver@...gle.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
rcu@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
"Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: Re: [PATCH 3/7] rcu/trace: Add name of the source for gp_seq
On Thu, Jun 18, 2020 at 03:19:01PM -0700, Paul E. McKenney wrote:
> On Thu, Jun 18, 2020 at 04:29:51PM -0400, Joel Fernandes (Google) wrote:
> > The gp_seq value can come from either of rdp, rsp or rnp.
> >
> > Only the rsp is the global source of truth (most accurate GP info). The
> > rnp can be off by ~1 and the rdp can be off by way more. Add some more
> > context to traces to clarify where it comes from.
>
> This would be better done in scripting that processes the trace messages.
> I must pass on this one.
I don't think so. I think people reading traces would get confused. Recently
I had to talk with someone about this as well when going over traces. I
myself struggle with it.
> For future reference, the TPS() around strings is not optional. Without
> it, trace messages from crash dumps are garbled, if I remember correctly.
Ok. I will fix that.
thanks,
- Joel
>
> Thanx, Paul
>
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > ---
> > include/trace/events/rcu.h | 12 ++++++++----
> > kernel/rcu/tree.c | 32 ++++++++++++++++----------------
> > kernel/rcu/tree_plugin.h | 2 +-
> > 3 files changed, 25 insertions(+), 21 deletions(-)
> >
> > diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
> > index a6d49864dcc27..cb5363564f7ed 100644
> > --- a/include/trace/events/rcu.h
> > +++ b/include/trace/events/rcu.h
> > @@ -68,24 +68,28 @@ TRACE_EVENT(rcu_utilization,
> > */
> > TRACE_EVENT_RCU(rcu_grace_period,
> >
> > - TP_PROTO(const char *rcuname, unsigned long gp_seq, const char *gpevent),
> > + TP_PROTO(const char *rcuname, const char *gp_seq_src,
> > + unsigned long gp_seq, const char *gpevent),
> >
> > - TP_ARGS(rcuname, gp_seq, gpevent),
> > + TP_ARGS(rcuname, gp_seq_src, gp_seq, gpevent),
> >
> > TP_STRUCT__entry(
> > __field(const char *, rcuname)
> > + __field(const char *, gp_seq_src)
> > __field(unsigned long, gp_seq)
> > __field(const char *, gpevent)
> > ),
> >
> > TP_fast_assign(
> > __entry->rcuname = rcuname;
> > + __entry->gp_seq_src = gp_seq_src;
> > __entry->gp_seq = gp_seq;
> > __entry->gpevent = gpevent;
> > ),
> >
> > - TP_printk("%s %lu %s",
> > - __entry->rcuname, __entry->gp_seq, __entry->gpevent)
> > + TP_printk("%s %s_gp_seq=%lu %s",
> > + __entry->rcuname, __entry->gp_seq_src,
> > + __entry->gp_seq, __entry->gpevent)
> > );
> >
> > /*
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index c61af6a33fbfd..81df1b837dd9d 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1334,7 +1334,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
> > trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
> > goto unlock_out;
> > }
> > - trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
> > + trace_rcu_grace_period(rcu_state.name, "rsp", data_race(rcu_state.gp_seq), TPS("newreq"));
> > ret = true; /* Caller must wake GP kthread. */
> > unlock_out:
> > /* Push furthest requested GP to leaf node and rcu_data structure. */
> > @@ -1437,9 +1437,9 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
> >
> > /* Trace depending on how much we were able to accelerate. */
> > if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
> > - trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccWaitCB"));
> > + trace_rcu_grace_period(rcu_state.name, "rdp", rdp->gp_seq, TPS("AccWaitCB"));
> > else
> > - trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccReadyCB"));
> > + trace_rcu_grace_period(rcu_state.name, "rdp", rdp->gp_seq, TPS("AccReadyCB"));
> >
> > /* Count CBs for tracing. */
> > rcu_segcblist_countseq(&rdp->cblist, cbs, gps);
> > @@ -1543,7 +1543,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
> > if (!offloaded)
> > ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
> > rdp->core_needs_qs = false;
> > - trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
> > + trace_rcu_grace_period(rcu_state.name, "rdp", rdp->gp_seq, TPS("cpuend"));
> > } else {
> > if (!offloaded)
> > ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
> > @@ -1559,7 +1559,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
> > * set up to detect a quiescent state, otherwise don't
> > * go looking for one.
> > */
> > - trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
> > + trace_rcu_grace_period(rcu_state.name, "rnp", rnp->gp_seq, TPS("cpustart"));
> > need_qs = !!(rnp->qsmask & rdp->grpmask);
> > rdp->cpu_no_qs.b.norm = need_qs;
> > rdp->core_needs_qs = need_qs;
> > @@ -1660,7 +1660,7 @@ static bool rcu_gp_init(void)
> > /* Record GP times before starting GP, hence rcu_seq_start(). */
> > rcu_seq_start(&rcu_state.gp_seq);
> > ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq, TPS("start"));
> > raw_spin_unlock_irq_rcu_node(rnp);
> >
> > /*
> > @@ -1828,7 +1828,7 @@ static void rcu_gp_fqs_loop(void)
> > WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
> > jiffies + (j ? 3 * j : 2));
> > }
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq,
> > TPS("fqswait"));
> > rcu_state.gp_state = RCU_GP_WAIT_FQS;
> > ret = swait_event_idle_timeout_exclusive(
> > @@ -1843,7 +1843,7 @@ static void rcu_gp_fqs_loop(void)
> > /* If time for quiescent-state forcing, do it. */
> > if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
> > (gf & RCU_GP_FLAG_FQS)) {
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq,
> > TPS("fqsstart"));
> > rcu_gp_fqs(first_gp_fqs);
> > gf = 0;
> > @@ -1851,7 +1851,7 @@ static void rcu_gp_fqs_loop(void)
> > first_gp_fqs = false;
> > gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
> > }
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq,
> > TPS("fqsend"));
> > cond_resched_tasks_rcu_qs();
> > WRITE_ONCE(rcu_state.gp_activity, jiffies);
> > @@ -1862,7 +1862,7 @@ static void rcu_gp_fqs_loop(void)
> > cond_resched_tasks_rcu_qs();
> > WRITE_ONCE(rcu_state.gp_activity, jiffies);
> > WARN_ON(signal_pending(current));
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq,
> > TPS("fqswaitsig"));
> > ret = 1; /* Keep old FQS timing. */
> > j = jiffies;
> > @@ -1945,7 +1945,7 @@ static void rcu_gp_cleanup(void)
> > raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
> >
> > /* Declare grace period done, trace first to use old GP number. */
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq, TPS("end"));
> > rcu_seq_end(&rcu_state.gp_seq);
> > ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
> > rcu_state.gp_state = RCU_GP_IDLE;
> > @@ -1962,7 +1962,7 @@ static void rcu_gp_cleanup(void)
> > if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
> > WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
> > WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
> > - trace_rcu_grace_period(rcu_state.name,
> > + trace_rcu_grace_period(rcu_state.name, "rsp",
> > rcu_state.gp_seq,
> > TPS("newreq"));
> > } else {
> > @@ -1982,7 +1982,7 @@ static int __noreturn rcu_gp_kthread(void *unused)
> >
> > /* Handle grace-period start. */
> > for (;;) {
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq,
> > TPS("reqwait"));
> > rcu_state.gp_state = RCU_GP_WAIT_GPS;
> > swait_event_idle_exclusive(rcu_state.gp_wq,
> > @@ -1996,7 +1996,7 @@ static int __noreturn rcu_gp_kthread(void *unused)
> > cond_resched_tasks_rcu_qs();
> > WRITE_ONCE(rcu_state.gp_activity, jiffies);
> > WARN_ON(signal_pending(current));
> > - trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> > + trace_rcu_grace_period(rcu_state.name, "rsp", rcu_state.gp_seq,
> > TPS("reqwaitsig"));
> > }
> >
> > @@ -2240,7 +2240,7 @@ int rcutree_dying_cpu(unsigned int cpu)
> > return 0;
> >
> > blkd = !!(rnp->qsmask & rdp->grpmask);
> > - trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
> > + trace_rcu_grace_period(rcu_state.name, "rsp", READ_ONCE(rnp->gp_seq),
> > blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
> > return 0;
> > }
> > @@ -3733,7 +3733,7 @@ int rcutree_prepare_cpu(unsigned int cpu)
> > rdp->core_needs_qs = false;
> > rdp->rcu_iw_pending = false;
> > rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
> > - trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
> > + trace_rcu_grace_period(rcu_state.name, "rdp", rdp->gp_seq, TPS("cpuonl"));
> > raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> > rcu_prepare_kthreads(cpu);
> > rcu_spawn_cpu_nocb_kthread(cpu);
> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> > index 982fc5be52698..32f761cf16c33 100644
> > --- a/kernel/rcu/tree_plugin.h
> > +++ b/kernel/rcu/tree_plugin.h
> > @@ -262,7 +262,7 @@ static void rcu_qs(void)
> > {
> > RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
> > if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
> > - trace_rcu_grace_period(TPS("rcu_preempt"),
> > + trace_rcu_grace_period(TPS("rcu_preempt"), "rdp",
> > __this_cpu_read(rcu_data.gp_seq),
> > TPS("cpuqs"));
> > __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
> > --
> > 2.27.0.111.gc72c7da667-goog
> >
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