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SubjectRe: [PATCH -rcu dev 2/2] rcu/dyntick-idle: Add better tracing
On Fri, Aug 30, 2019 at 12:23:48PM -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 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.
>
> 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@joelfernandes.org>

This looks fine, but depends on the earlier patch.

Thanx, Paul

> ---
> 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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