linux-kernel - Re: [PATCH tip/core/rcu 5/7] torture: Trace long read-side delays

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Message-ID: <20161114185452.6fm4ktoevs3gpvoq@x>
Date:   Mon, 14 Nov 2016 10:54:52 -0800
From:   Josh Triplett <josh@...htriplett.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 5/7] torture: Trace long read-side delays

On Mon, Nov 14, 2016 at 10:44:21AM -0800, Paul E. McKenney wrote:
> On Mon, Nov 14, 2016 at 09:21:10AM -0800, Josh Triplett wrote:
> > On Mon, Nov 14, 2016 at 08:57:11AM -0800, Paul E. McKenney wrote:
> > > Although rcutorture will occasionally do a 50-millisecond grace-period
> > > delay, these delays are quite rare.  And rightly so, because otherwise
> > > the read rate would be quite low.  Thie means that it can be important
> > > to identify whether or not a given run contained a long-delay read.
> > > This commit therefore inserts a trace_rcu_torture_read() event to flag
> > > runs containing long delays.
> > > 
> > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > A couple of apparent typos below.  With those fixed:
> > Reviewed-by: Josh Triplett <josh@...htriplett.org>
> > 
> > >  include/trace/events/rcu.h |  5 ++++-
> > >  kernel/rcu/rcutorture.c    | 11 ++++++++++-
> > >  2 files changed, 14 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
> > > index d3e756539d44..b31e05bc8e26 100644
> > > --- a/include/trace/events/rcu.h
> > > +++ b/include/trace/events/rcu.h
> > > @@ -698,7 +698,10 @@ TRACE_EVENT(rcu_batch_end,
> > >  /*
> > >   * Tracepoint for rcutorture readers.  The first argument is the name
> > >   * of the RCU flavor from rcutorture's viewpoint and the second argument
> > > - * is the callback address.
> > > + * is the callback address.  The third callback is the start time in
> > > + * seconds, and the last two arguments are the grace period numbers
> > > + * and the beginning and end of the read, respectively.  Note that the
> > > + * callback address can be NULL.
> > 
> > s/third callback/third argument/?
> 
> Good catch, fixed!
> 
> > Also, s/and the beginning/of the beginning/?
> 
> Let's see...  "the last two arguments are the grace period numbers and
> the beginning and end of the read, respectively."  -ENONSENSE for sure.
> 
> I believe that the "and" needs to become "at" as follows:
> 
> "the last two arguments are the grace period numbers at the beginning
> and end of the read, respectively."
> 
> Does that help?

That works, yes.