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

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Message-ID: <20140507212015.GB27924@cloud>
Date:	Wed, 7 May 2014 14:20:15 -0700
From:	josh@...htriplett.org
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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 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?

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