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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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