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Message-ID: <20190828230538.GD26530@linux.ibm.com>
Date: Wed, 28 Aug 2019 16:05:38 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc: linux-kernel@...r.kernel.org,
Frederic Weisbecker <fweisbec@...il.com>,
Jonathan Corbet <corbet@....net>,
Josh Triplett <josh@...htriplett.org>, kernel-team@...roid.com,
Lai Jiangshan <jiangshanlai@...il.com>,
linux-doc@...r.kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
rcu@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] rcu/dyntick-idle: Add better tracing
On Wed, Aug 28, 2019 at 02:26:13PM -0400, Joel Fernandes (Google) wrote:
> The dyntick-idle traces are a bit confusing. This patch makes it simpler
> and adds some missing cases such as EQS-enter because 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.
>
> This patch is based on the previous patches to simplify rcu_dyntick
> counters [1] and with these traces, I have verified the counters are
> working properly.
>
> [1]
> Link: https://lore.kernel.org/patchwork/patch/1120021/
> Link: https://lore.kernel.org/patchwork/patch/1120022/
>
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Looks plausible to me.
Thanx, Paul
> ---
> include/trace/events/rcu.h | 13 ++++++++-----
> kernel/rcu/tree.c | 17 +++++++++++------
> 2 files changed, 19 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 1465a3e406f8..1a65919ec800 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -570,7 +570,8 @@ 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);
> @@ -642,15 +643,17 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
> * leave it in non-RCU-idle state.
> */
> if (rdp->dynticks_nesting != 1) {
> - trace_rcu_dyntick(TPS("--="), rdp->dynticks_nesting,
> - rdp->dynticks_nesting - 2, rdp->dynticks);
> + trace_rcu_dyntick(TPS("StillNonIdle"), TPS("IRQ"),
> + rdp->dynticks_nesting, rdp->dynticks_nesting - 2,
> + rdp->dynticks);
> WRITE_ONCE(rdp->dynticks_nesting, /* No store tearing. */
> rdp->dynticks_nesting - 2);
> return;
> }
>
> /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
> - trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nesting, 0, rdp->dynticks);
> + trace_rcu_dyntick(TPS("Start"), TPS("IRQ"), rdp->dynticks_nesting, 0,
> + rdp->dynticks);
> WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid store tearing. */
>
> if (irq)
> @@ -733,7 +736,8 @@ 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);
>
> @@ -825,7 +829,8 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
> tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
> }
>
> - trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
> + trace_rcu_dyntick(incby == 1 ? TPS("End") : TPS("StillNonIdle"),
> + TPS("IRQ"),
> rdp->dynticks_nesting,
> rdp->dynticks_nesting + incby, rdp->dynticks);
>
> --
> 2.23.0.187.g17f5b7556c-goog
>
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