linux-kernel - Re: [PATCH tip/core/rcu 16/86] rcu: make rcutorture version numbers available through debugfs

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Date:	Mon, 2 May 2011 10:39:56 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	patches@...aro.org, "Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 16/86] rcu: make rcutorture version numbers
 available through debugfs

On Mon, May 02, 2011 at 01:30:24AM -0700, Paul E. McKenney wrote:
> On Sun, May 01, 2011 at 08:29:03AM -0700, Josh Triplett wrote:
> > On Sun, May 01, 2011 at 06:20:56AM -0700, Paul E. McKenney wrote:
> > > From: Paul E. McKenney <paul.mckenney@...aro.org>
> > > 
> > > It is not possible to accurately correlate rcutorture output with that
> > > of debugfs.  This patch therefore adds a debugfs file that prints out
> > > the rcutorture version number, permitting easy correlation.
> > 
> > You can't accurately correlate debugfs values with each
> > other, either, right?  The rcutorture version number can change between
> > accesses to different debugfs files.
> 
> True, but this is OK given the use case.
> 
> The problem that I used to have was that an automated test run would get
> a grace-period hang somewhere in the middle of a long run.  Now, in a
> grace-period hang, most of the interesting debugfs output is static,
> so it is not necessary to line them up exactly.  All that is needed is
> for the corellation to be good enough for me to ignore the debugfs
> output that came a long time before the hang started.
> 
> Also, if there is an RCU grace-period hang, the rcutorture version number
> will stop changing once it has the entire array waiting for a grace period,
> which normally happens in a few seconds.
> 
> Make sense, or am I missing your point?

Makes sense.

- Josh Triplett
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