linux-kernel - Re: [PATCH v9 4/7] rcu/trace: Add tracing for how segcb list changes

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Date:   Wed, 11 Nov 2020 08:49:41 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rcu@...r.kernel.org, "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        fweisbec@...il.com, neeraj.iitr10@...il.com
Subject: Re: [PATCH v9 4/7] rcu/trace: Add tracing for how segcb list
 changes

On Tue, 10 Nov 2020 16:35:30 -0800
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> > +void __trace_rcu_segcb_stats(struct rcu_segcblist *rsclp, const char *context)
> > +{
> > +	int cbs[RCU_CBLIST_NSEGS];
> > +	unsigned long gps[RCU_CBLIST_NSEGS];
> > +
> > +	if (!trace_rcu_segcb_stats_enabled())
> > +		return;  
> 
> Can't you rely on the trace system to enable and disable this trace
> event?  If the thought is to save instructions, then moving all this
> into TP_fast_assign() enables the trace system to deal with that as well.
> 
> > +	rcu_segcblist_countseq(rsclp, cbs, gps);
> > +
> > +	trace_rcu_segcb_stats(context, cbs, gps);
> > +}
> > +#endif

Yeah, I agree with Paul. I think it is possible to move this all into the
TP_fast_assign. If you have trouble doing so, let me know.

-- Steve