Re: [PATCH -rcu dev 2/2] rcu/dyntick-idle: Add better tracing

[Joel Fernandes <joel@joelfernandes.org>]

On Tue, Sep 03, 2019 at 01:04:46PM -0700, Paul E. McKenney wrote:
> 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.

The earlier patch looks Ok? Did not see any review comments. That is just a
revert of an old commit.

thanks,

 - Joel

> 							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
> >