linux-kernel - Re: [PATCH tip/core/rcu 06/45] torture: Intensify locking test

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Date:	Wed, 7 May 2014 16:56:33 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	josh@...htriplett.org
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, oleg@...hat.com, sbw@....edu
Subject: Re: [PATCH tip/core/rcu 06/45] torture: Intensify locking test

On Wed, May 07, 2014 at 02:20:15PM -0700, josh@...htriplett.org wrote:
> On Mon, Apr 28, 2014 at 05:24:54PM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > 
> > The current lock_torture_writer() spends too much time sleeping and not
> > enough time hammering locks, as in an eight-CPU test will often only be
> > utilizing a CPU or two.  This commit therefore makes lock_torture_writer()
> > sleep less and hammer more.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  kernel/locking/locktorture.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> > index f26b1a18e34e..b0d3e3c50672 100644
> > --- a/kernel/locking/locktorture.c
> > +++ b/kernel/locking/locktorture.c
> > @@ -219,7 +219,8 @@ static int lock_torture_writer(void *arg)
> >  	set_user_nice(current, 19);
> >  
> >  	do {
> > -		schedule_timeout_uninterruptible(1);
> > +		if ((torture_random(&rand) & 0xfffff) == 0)
> > +			schedule_timeout_uninterruptible(1);
> 
> That's a one-in-1048576 chance of sleeping for a jiffy; is that frequent
> enough to even bother sleeping at all?

On large systems, maybe not.  Smallish systems should be able to get
through that loop a million times in a few hundreds of milliseconds,
though.  So longer term a smarter approach might be needed, but this
should be a good start.

							Thanx, Paul

> >  		cur_ops->writelock();
> >  		if (WARN_ON_ONCE(lock_is_write_held))
> >  			lwsp->n_write_lock_fail++;
> > -- 
> > 1.8.1.5
> > 
> 

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