Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 16 Nov 2011 12:32:26 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 2/9] rcu: Add rcutorture system-shutdown capability |
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On Tue, Nov 15, 2011 at 01:46:15PM -0800, Josh Triplett wrote: > 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.
For some things, the init= parameter does work great. I do intend to use it when collecting event-tracing and debugfs data, for example.
However, there is still a need for RCU torture testing that will operate correctly regardless of how userspace is set up. That, and there are quite a few different kernel test setup, each with their own peculiar capabilities and limitations. So what happened was that before people suggested the init= approach, I implemented enough of the in-kernel approach to appreciate how much it simplifies life for the common case of "just torture-test RCU". As in I should have done this long ago.
I will therefore be taking both approaches. There will be at least one more patch pushing what is now script into rcutorture.c.
> > --- 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.
Turns out that my initial patch added another variable that I explicitly initialized to zero. Of course, checkpatch yelled at me about this, so I figured I should fix the other nearby occurrences of this while I was at it. Doesn't really seem to me to be worth a separate patch, though.
> > @@ -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.
Or maybe a copy-paste stutter. ;-)
Good eyes, fixed!
> > +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?)
It actually did help me find a bug where it was failing to shut down. I could use different code paths, but that would defeat the debugging.
So I increased the sleep time to 30 seconds. Fair enough?
> > + 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?
Only if we are shutting down. And the alternative is a deadlock where this task invokes kthread_stop() on itself. ;-)
> > + 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.
Indeed, gcc yelled at me, so I added the "return 0". ;-)
Thanx, Paul
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