Re: [PATCH 3/3] rcu/trace: Add name of the source for gp_seq to prevent confusion

Paul E. McKenney
2020-06-20T15:45:21Z

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