Message-ID: <20060822051303.GB12787@us.ibm.com>
Date:	Mon, 21 Aug 2006 22:13:03 -0700
From:	"Paul E. McKenney" <paulmck@...ibm.com>
To:	Josh Triplett <josht@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	Dipkanar Sarma <dipankar@...ibm.com>,
	Adrian Bunk <bunk@...sta.de>
Subject: Re: [PATCH v2] RCU: add fake writers to rcutorture

On Mon, Aug 21, 2006 at 03:25:42PM -0700, Josh Triplett wrote:
> rcutorture currently has one writer and an arbitrary number of readers.  To
> better exercise some of the code paths in RCU, add fake writer threads which
> call the synchronize function for the RCU variant in a loop, with a delay
> between calls to arrange for different numbers of writers running in parallel.

Looks like a very good addition to the torturing of RCU!!!

Acked-by: Paul E. McKenney <paulmck@...ibm.com>
> Signed-off-by: Josh Triplett <josh@...edesktop.org>
> ---
> This revised patch incorporates Adrian Bunk's suggestion to make
> rcu_bh_torture_synchronize() static, and adds the previously missing
> Signed-Off-By noticed by Andrew Morton.  Please replace the -mm patch
> "rcu-add-fake-writers-to-rcutorture.patch" with this one.
> 
> I've tested rcutorture with this patch against classic RCU, the _bh
> variant, and SRCU.  In the SRCU case, I used a systemtap script to
> confirm that the fakewriters do trigger the early return case in
> synchronize_srcu().
> 
>  Documentation/RCU/torture.txt |    9 +++
>  kernel/rcutorture.c           |  109 +++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 113 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
> index 2174bad..2180ef9 100644
> --- a/Documentation/RCU/torture.txt
> +++ b/Documentation/RCU/torture.txt
> @@ -28,6 +28,15 @@ nreaders	This is the number of RCU readi
>  		To properly exercise RCU implementations with preemptible
>  		read-side critical sections.
>  
> +nfakewriters	This is the number of RCU fake writer threads to run.  Fake
> +		writer threads repeatedly use the synchronous "wait for
> +		current readers" function of the interface selected by
> +		torture_type, with a delay between calls to allow for various
> +		different numbers of writers running in parallel.
> +		nfakewriters defaults to 4, which provides enough parallelism
> +		to trigger special cases caused by multiple writers, such as
> +		the synchronize_srcu() early return optimization.
> +
>  stat_interval	The number of seconds between output of torture
>  		statistics (via printk()).  Regardless of the interval,
>  		statistics are printed when the module is unloaded.
> diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
> index 43d6d4f..e045021 100644
> --- a/kernel/rcutorture.c
> +++ b/kernel/rcutorture.c
> @@ -15,9 +15,10 @@
>   * along with this program; if not, write to the Free Software
>   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
>   *
> - * Copyright (C) IBM Corporation, 2005
> + * Copyright (C) IBM Corporation, 2005, 2006
>   *
>   * Authors: Paul E. McKenney <paulmck@...ibm.com>
> + *          Josh Triplett <josh@...edesktop.org>
>   *
>   * See also:  Documentation/RCU/torture.txt
>   */
> @@ -47,9 +48,11 @@ #include <linux/stat.h>
>  #include <linux/srcu.h>
>  
>  MODULE_LICENSE("GPL");
> -MODULE_AUTHOR("Paul E. McKenney <paulmck@...ibm.com>");
> +MODULE_AUTHOR("Paul E. McKenney <paulmck@...ibm.com> and "
> +              "Josh Triplett <josh@...edesktop.org>");
>  
>  static int nreaders = -1;	/* # reader threads, defaults to 2*ncpus */
> +static int nfakewriters = 4;	/* # fake writer threads */
>  static int stat_interval;	/* Interval between stats, in seconds. */
>  				/*  Defaults to "only at end of test". */
>  static int verbose;		/* Print more debug info. */
> @@ -59,6 +62,8 @@ static char *torture_type = "rcu"; /* Wh
>  
>  module_param(nreaders, int, 0);
>  MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");
> +module_param(nfakewriters, int, 0);
> +MODULE_PARM_DESC(nfakewriters, "Number of RCU fake writer threads");
>  module_param(stat_interval, int, 0);
>  MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");
>  module_param(verbose, bool, 0);
> @@ -82,6 +87,7 @@ static char printk_buf[4096];
>  
>  static int nrealreaders;
>  static struct task_struct *writer_task;
> +static struct task_struct **fakewriter_tasks;
>  static struct task_struct **reader_tasks;
>  static struct task_struct *stats_task;
>  static struct task_struct *shuffler_task;
> @@ -186,6 +192,7 @@ struct rcu_torture_ops {
>  	void (*readunlock)(int idx);
>  	int (*completed)(void);
>  	void (*deferredfree)(struct rcu_torture *p);
> +	void (*sync)(void);
>  	int (*stats)(char *page);
>  	char *name;
>  };
> @@ -258,6 +265,7 @@ static struct rcu_torture_ops rcu_ops = 
>  	.readunlock = rcu_torture_read_unlock,
>  	.completed = rcu_torture_completed,
>  	.deferredfree = rcu_torture_deferred_free,
> +	.sync = synchronize_rcu,
>  	.stats = NULL,
>  	.name = "rcu"
>  };
> @@ -287,6 +295,28 @@ static void rcu_bh_torture_deferred_free
>  	call_rcu_bh(&p->rtort_rcu, rcu_torture_cb);
>  }
>  
> +struct rcu_bh_torture_synchronize {
> +	struct rcu_head head;
> +	struct completion completion;
> +};
> +
> +static void rcu_bh_torture_wakeme_after_cb(struct rcu_head *head)
> +{
> +	struct rcu_bh_torture_synchronize *rcu;
> +
> +	rcu = container_of(head, struct rcu_bh_torture_synchronize, head);
> +	complete(&rcu->completion);
> +}
> +
> +static void rcu_bh_torture_synchronize(void)
> +{
> +	struct rcu_bh_torture_synchronize rcu;
> +
> +	init_completion(&rcu.completion);
> +	call_rcu_bh(&rcu.head, rcu_bh_torture_wakeme_after_cb);
> +	wait_for_completion(&rcu.completion);
> +}
> +
>  static struct rcu_torture_ops rcu_bh_ops = {
>  	.init = NULL,
>  	.cleanup = NULL,
> @@ -295,6 +325,7 @@ static struct rcu_torture_ops rcu_bh_ops
>  	.readunlock = rcu_bh_torture_read_unlock,
>  	.completed = rcu_bh_torture_completed,
>  	.deferredfree = rcu_bh_torture_deferred_free,
> +	.sync = rcu_bh_torture_synchronize,
>  	.stats = NULL,
>  	.name = "rcu_bh"
>  };
> @@ -367,6 +398,11 @@ static void srcu_torture_deferred_free(s
>  	}
>  }
>  
> +static void srcu_torture_synchronize(void)
> +{
> +	synchronize_srcu(&srcu_ctl);
> +}
> +
>  static int srcu_torture_stats(char *page)
>  {
>  	int cnt = 0;
> @@ -392,6 +428,7 @@ static struct rcu_torture_ops srcu_ops =
>  	.readunlock = srcu_torture_read_unlock,
>  	.completed = srcu_torture_completed,
>  	.deferredfree = srcu_torture_deferred_free,
> +	.sync = srcu_torture_synchronize,
>  	.stats = srcu_torture_stats,
>  	.name = "srcu"
>  };
> @@ -444,6 +481,30 @@ rcu_torture_writer(void *arg)
>  }
>  
>  /*
> + * RCU torture fake writer kthread.  Repeatedly calls sync, with a random
> + * delay between calls.
> + */
> +static int
> +rcu_torture_fakewriter(void *arg)
> +{
> +	DEFINE_RCU_RANDOM(rand);
> +
> +	VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task started");
> +	set_user_nice(current, 19);
> +
> +	do {
> +		schedule_timeout_uninterruptible(1 + rcu_random(&rand)%10);
> +		udelay(rcu_random(&rand) & 0x3ff);
> +		cur_ops->sync();
> +	} while (!kthread_should_stop() && !fullstop);
> +
> +	VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task stopping");
> +	while (!kthread_should_stop())
> +		schedule_timeout_uninterruptible(1);
> +	return 0;
> +}
> +
> +/*
>   * RCU torture reader kthread.  Repeatedly dereferences rcu_torture_current,
>   * incrementing the corresponding element of the pipeline array.  The
>   * counter in the element should never be greater than 1, otherwise, the
> @@ -621,6 +682,12 @@ static void rcu_torture_shuffle_tasks(vo
>  				set_cpus_allowed(reader_tasks[i], tmp_mask);
>  	}
>  
> +	if (fakewriter_tasks != NULL) {
> +		for (i = 0; i < nfakewriters; i++)
> +			if (fakewriter_tasks[i])
> +				set_cpus_allowed(fakewriter_tasks[i], tmp_mask);
> +	}
> +
>  	if (writer_task)
>  		set_cpus_allowed(writer_task, tmp_mask);
>  
> @@ -654,11 +721,12 @@ rcu_torture_shuffle(void *arg)
>  static inline void
>  rcu_torture_print_module_parms(char *tag)
>  {
> -	printk(KERN_ALERT "%s" TORTURE_FLAG "--- %s: nreaders=%d "
> +	printk(KERN_ALERT "%s" TORTURE_FLAG
> +		"--- %s: nreaders=%d nfakewriters=%d "
>  		"stat_interval=%d verbose=%d test_no_idle_hz=%d "
>  		"shuffle_interval = %d\n",
> -		torture_type, tag, nrealreaders, stat_interval, verbose,
> -		test_no_idle_hz, shuffle_interval);
> +		torture_type, tag, nrealreaders, nfakewriters,
> +		stat_interval, verbose, test_no_idle_hz, shuffle_interval);
>  }
>  
>  static void
> @@ -693,6 +761,19 @@ rcu_torture_cleanup(void)
>  	}
>  	rcu_torture_current = NULL;
>  
> +	if (fakewriter_tasks != NULL) {
> +		for (i = 0; i < nfakewriters; i++) {
> +			if (fakewriter_tasks[i] != NULL) {
> +				VERBOSE_PRINTK_STRING(
> +					"Stopping rcu_torture_fakewriter task");
> +				kthread_stop(fakewriter_tasks[i]);
> +			}
> +			fakewriter_tasks[i] = NULL;
> +		}
> +		kfree(fakewriter_tasks);
> +		fakewriter_tasks = NULL;
> +	}
> +
>  	if (stats_task != NULL) {
>  		VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
>  		kthread_stop(stats_task);
> @@ -780,6 +861,24 @@ rcu_torture_init(void)
>  		writer_task = NULL;
>  		goto unwind;
>  	}
> +	fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),
> +	                           GFP_KERNEL);
> +	if (fakewriter_tasks == NULL) {
> +		VERBOSE_PRINTK_ERRSTRING("out of memory");
> +		firsterr = -ENOMEM;
> +		goto unwind;
> +	}
> +	for (i = 0; i < nfakewriters; i++) {
> +		VERBOSE_PRINTK_STRING("Creating rcu_torture_fakewriter task");
> +		fakewriter_tasks[i] = kthread_run(rcu_torture_fakewriter, NULL,
> +		                                  "rcu_torture_fakewriter");
> +		if (IS_ERR(fakewriter_tasks[i])) {
> +			firsterr = PTR_ERR(fakewriter_tasks[i]);
> +			VERBOSE_PRINTK_ERRSTRING("Failed to create fakewriter");
> +			fakewriter_tasks[i] = NULL;
> +			goto unwind;
> +		}
> +	}
>  	reader_tasks = kzalloc(nrealreaders * sizeof(reader_tasks[0]),
>  			       GFP_KERNEL);
>  	if (reader_tasks == NULL) {
> -- 
> 1.4.1.1
> 
> 
-
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