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SubjectRe: [PATCH tip/core/rcu 2/9] rcu: Add rcutorture system-shutdown capability
On Tue, Nov 15, 2011 at 12:27:58PM -0800, Paul E. McKenney wrote:
> From: Paul E. McKenney <paul.mckenney@linaro.org>
>
> Although it is easy to run rcutorture tests under KVM, there is currently
> no nice way to run such a test for a fixed time period, collect all of
> the rcutorture data, and then shut the system down cleanly. This commit
> therefore adds an rcutorture module parameter named "shutdown_secs" that
> specified the run duration in seconds, after which rcutorture terminates
> the test and powers the system down. The default value for "shutdown_secs"
> is zero, which disables shutdown.
>
> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

From your recent post on this, I thought you found a solution through
the init= parameter, which seems preferable.

> --- a/kernel/rcutorture.c
> +++ b/kernel/rcutorture.c
> @@ -61,9 +61,10 @@ static int test_no_idle_hz; /* Test RCU's support for tickless idle CPUs. */
> static int shuffle_interval = 3; /* Interval between shuffles (in sec)*/
> static int stutter = 5; /* Start/stop testing interval (in sec) */
> static int irqreader = 1; /* RCU readers from irq (timers). */
> -static int fqs_duration = 0; /* Duration of bursts (us), 0 to disable. */
> -static int fqs_holdoff = 0; /* Hold time within burst (us). */
> +static int fqs_duration; /* Duration of bursts (us), 0 to disable. */
> +static int fqs_holdoff; /* Hold time within burst (us). */

Looks like these lines picked up unrelated whitespace changes in this
commit.

> @@ -1305,6 +1313,37 @@ static int rcutorture_booster_init(int cpu)
> return 0;
> }
>
> +/*
> + * Cause the rcutorture test to "stutter", starting and stopping all
> + * threads periodically.
> + */

This comment looks like a copy-paste error.

> +static int
> +rcu_torture_shutdown(void *arg)
> +{
> + VERBOSE_PRINTK_STRING("rcu_torture_shutdown task started");
> + while (ULONG_CMP_LT(jiffies, shutdown_time) &&
> + !kthread_should_stop()) {
> + if (verbose)
> + printk(KERN_ALERT "%s" TORTURE_FLAG
> + "rcu_torture_shutdown task: %lu "
> + "jiffies remaining\n",
> + torture_type, shutdown_time - jiffies);
> + schedule_timeout_interruptible(HZ);
> + }

Any particular reason to wake up once a second here? If !verbose, this could just
sleep until shutdown time. (And does the verbose output really help
here, given printk timestamps?)

> + if (ULONG_CMP_LT(jiffies, shutdown_time)) {
> + VERBOSE_PRINTK_STRING("rcu_torture_shutdown task stopping");
> + return 0;
> + }
> +
> + /* OK, shut down the system. */
> +
> + VERBOSE_PRINTK_STRING("rcu_torture_shutdown task shutting down system");
> + shutdown_task = NULL; /* Avoid self-kill deadlock. */

Not that it matters much here, but won't this cause a leak?

> + rcu_torture_cleanup(); /* Get the success/failure message. */
> + kernel_power_off(); /* Shut down the system. */
> + return 0;
> +}

Huh. I would have expected kernel_power_off to use noreturn, making the
return 0 unnecessary here; however, apparently it doesn't.

- Josh Triplett


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