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Subject[PATCH v2 -rcu dev 2/2] rcu/dyntick-idle: Add better tracing
Date
The dyntick-idle traces are a bit confusing. This patch makes it simpler
and adds some missing cases such as EQS-enter due to user vs idle mode.

Following are the changes:
(1) Add a new context field to trace_rcu_dyntick tracepoint. This
context field can be "USER", "IDLE" or "IRQ".

(2) Remove the "++=" and "--=" strings and replace them with
"StillNonIdle". This is much easier on the eyes, and the -- and ++
are easily apparent in the dynticks_nesting counters we are printing
anyway.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
include/trace/events/rcu.h | 13 ++++++++-----
kernel/rcu/tree.c | 19 +++++++++++++------
2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 66122602bd08..474c1f7e7104 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -449,12 +449,14 @@ TRACE_EVENT_RCU(rcu_fqs,
*/
TRACE_EVENT_RCU(rcu_dyntick,

- TP_PROTO(const char *polarity, long oldnesting, long newnesting, atomic_t dynticks),
+ TP_PROTO(const char *polarity, const char *context, long oldnesting,
+ long newnesting, atomic_t dynticks),

- TP_ARGS(polarity, oldnesting, newnesting, dynticks),
+ TP_ARGS(polarity, context, oldnesting, newnesting, dynticks),

TP_STRUCT__entry(
__field(const char *, polarity)
+ __field(const char *, context)
__field(long, oldnesting)
__field(long, newnesting)
__field(int, dynticks)
@@ -462,14 +464,15 @@ TRACE_EVENT_RCU(rcu_dyntick,

TP_fast_assign(
__entry->polarity = polarity;
+ __entry->context = context;
__entry->oldnesting = oldnesting;
__entry->newnesting = newnesting;
__entry->dynticks = atomic_read(&dynticks);
),

- TP_printk("%s %lx %lx %#3x", __entry->polarity,
- __entry->oldnesting, __entry->newnesting,
- __entry->dynticks & 0xfff)
+ TP_printk("%s %s %lx %lx %#3x", __entry->polarity,
+ __entry->context, __entry->oldnesting, __entry->newnesting,
+ __entry->dynticks & 0xfff)
);

/*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 417dd00b9e87..463407762b5a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -533,7 +533,8 @@ static void rcu_eqs_enter(bool user)
}

lockdep_assert_irqs_disabled();
- trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, rdp->dynticks);
+ trace_rcu_dyntick(TPS("Start"), (user ? TPS("USER") : TPS("IDLE")),
+ rdp->dynticks_nesting, 0, rdp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
rdp = this_cpu_ptr(&rcu_data);
do_nocb_deferred_wakeup(rdp);
@@ -606,14 +607,17 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
* leave it in non-RCU-idle state.
*/
if (rdp->dynticks_nmi_nesting != 1) {
- trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
+ trace_rcu_dyntick(TPS("StillNonIdle"), TPS("IRQ"),
+ rdp->dynticks_nmi_nesting,
+ rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
rdp->dynticks_nmi_nesting - 2);
return;
}

/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
- trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, rdp->dynticks);
+ trace_rcu_dyntick(TPS("Start"), TPS("IRQ"), rdp->dynticks_nmi_nesting,
+ 0, rdp->dynticks);
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */

if (irq)
@@ -700,7 +704,8 @@ static void rcu_eqs_exit(bool user)
rcu_dynticks_task_exit();
rcu_dynticks_eqs_exit();
rcu_cleanup_after_idle();
- trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, rdp->dynticks);
+ trace_rcu_dyntick(TPS("End"), (user ? TPS("USER") : TPS("IDLE")),
+ rdp->dynticks_nesting, 1, rdp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
WRITE_ONCE(rdp->dynticks_nesting, 1);
WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
@@ -787,9 +792,11 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
rdp->rcu_forced_tick = true;
tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
}
- trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
- rdp->dynticks_nmi_nesting,
+
+ trace_rcu_dyntick(incby == 1 ? TPS("End") : TPS("StillNonIdle"),
+ TPS("IRQ"), rdp->dynticks_nmi_nesting,
rdp->dynticks_nmi_nesting + incby, rdp->dynticks);
+
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
rdp->dynticks_nmi_nesting + incby);
barrier();
--
2.23.0.187.g17f5b7556c-goog
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