linux-kernel - Re: [PATCH 3/3] rcu/trace: Add name of the source for gp

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Message-ID: <20200620154517.GA14328@paulmck-ThinkPad-P72>
Date:   Sat, 20 Jun 2020 08:45:17 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.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 3/3] rcu/trace: Add name of the source for gp_seq to
 prevent confusion

On Sat, Jun 20, 2020 at 01:36:08AM -0400, Joel Fernandes wrote:
> On Fri, Jun 19, 2020 at 10:40:01AM -0700, Paul E. McKenney wrote:
> > On Thu, Jun 18, 2020 at 10:07:18PM -0400, Joel Fernandes wrote:
> > > On Thu, Jun 18, 2020 at 09:36:41PM -0400, Joel Fernandes (Google) wrote:
> > > [...]
> > > > @@ -2019,7 +2019,7 @@ 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, TPS("rsp"), rcu_state.gp_seq,
> > > >  					       TPS("reqwaitsig"));
> > > >  		}
> > > >  
> > > > @@ -2263,7 +2263,7 @@ 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, TPS("rsp"), READ_ONCE(rnp->gp_seq),
> > > 
> > > This should be: TPS("rnp")  :-(
> > > 
> > > Happy to fix it up and resend if you'd like. Thanks!
> > 
> > I queued and pushed 1/2 and 2/2.
> 
> Thanks!
> 
> > but again, I am still not at all
> > convinced by 3/3.  If you want to make RCU trace output human
> > readable, post-processing will be needed.
> 
> Or I could post-process the code before building it since the pattern seems
> easy to parse ;-)

For this one thing, perhaps.  For most other information of interest,
doing so in-kernel would not be so good, for example, from a
lock-contention viewpoint.

							Thanx, Paul