Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 11 May 2018 09:24:43 -0700
From:   "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org, mingo@kernel.org,
        jiangshanlai@gmail.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
        rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
        fweisbec@gmail.com, oleg@redhat.com, joel.opensrc@gmail.com,
        torvalds@linux-foundation.org, npiggin@gmail.com
Subject: Re: [tip/core/rcu, 05/21] rcu: Make rcu_gp_cleanup() more accurately
 predict need for new GP
Reply-To: paulmck@linux.vnet.ibm.com
References: <1524452624-27589-5-git-send-email-paulmck@linux.vnet.ibm.com>
 <20180510072133.GA122810@joelaf.mtv.corp.google.com>
 <20180510131546.GN26088@linux.vnet.ibm.com>
 <20180510173754.GB228531@joelaf.mtv.corp.google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180510173754.GB228531@joelaf.mtv.corp.google.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Message-Id: <20180511162443.GA26088@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, May 10, 2018 at 10:37:54AM -0700, Joel Fernandes wrote:
> On Thu, May 10, 2018 at 06:15:46AM -0700, Paul E. McKenney wrote:
> [...] 
> > > Also in rcu_future_gp_cleanup, we call:
> > > 	trace_rcu_future_gp(rnp, rdp, c,
> > > 			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));
> > > For this case, in the final trace event record, rnp->completed and c will be
> > > the same, since c is set to rnp->completed before calling
> > > trace_rcu_future_gp. I was thinking they should be different, do you expect
> > > them to be the same?
> > 
> > Hmmm...  That does look a bit inconsistent.  And it currently uses
> > rnp->gp_seq instead of rnp->gp_seq_needed despite having the same
> > "CleanupMore" name.
> > 
> > Looks like a review of the calls to trace_rcu_this_gp() is in order.
> 
> I see you changed trace_rcu_future_gp to use trace_rcu_this_gp in 15/21.. I
> am not sure if the concern is still valid then since you seem to be correctly
> getting the future GP in those cases, except for the naming which I suggest
> be changed from 'c' to 'future_gp' just for clarity / self-documenting code.

Indeed, "c" for "->completed" is completely outdated.  ;-)

Would you be willing to send a patch providing a better name?

								Thanx, Paul