Messages in this thread | | | Date | Wed, 16 Nov 2011 15:43:58 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 2/9] rcu: Add rcutorture system-shutdown capability |
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On Wed, Nov 16, 2011 at 02:58:56PM -0800, Josh Triplett wrote: > On Wed, Nov 16, 2011 at 02:44:47PM -0800, Paul E. McKenney wrote: > > On Wed, Nov 16, 2011 at 02:15:45PM -0800, Josh Triplett wrote: > > > On Wed, Nov 16, 2011 at 12:32:26PM -0800, Paul E. McKenney wrote: > > > > 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. > > > > > > Seems like it would work just as easily to point init at a statically > > > linked C program which just sleeps for a fixed time and then shuts down. > > > However, given the special-purpose nature of rcutorture, I won't > > > complain that strongly. > > > > I did consider a statically linked C program, but that can introduce the > > need for cross-compilation into situations that do not otherwise need it. > > Wouldn't you need to cross-compile the kernel anyway in such situations?
Not necessarily, consider for example ABAT. (IBM-specific test setup for those unfamiliar with it -- related to autotest.)
I suspect that the only way for you to be convinced is for you to write a script that takes your preferred approach for injecting a test into (say) a KVM instance.
Then compare that script to adding a few parameters to the boot line, namely: "rcutorture.stat_interval=15 rcutorture.shutdown_secs=3600 rcutorture.rcutorture_runnable=1". ;-)
Using the parameters allows me to not care about the filesystem type, any need to fsck, instruction set, the distro, and even the type of userspace. Highly recommended!
> > > > > > +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? > > > > > > Well, now that you've debugged rcutorture's shutdown routine, would it > > > suffice to have a printk when you actually go to shut down, without > > > waking up for previous printks when not shutting down yet? > > > > > > (The poll time doesn't really matter, and sleeping for 30 seconds before > > > checking the time means you might overshoot by up to 30 seconds. I'd > > > like to avoid polling to begin with when you know exactly how long you > > > need to sleep.) > > > > Indeed, good points! But please see below for what this function turns > > into when taking that approach. > > See below for responses; that version seems like an improvement, though > it could still improve further. > > > rcu_torture_shutdown(void *arg) > > { > > long delta; > > unsigned long jiffies_snap; > > > > VERBOSE_PRINTK_STRING("rcu_torture_shutdown task started"); > > jiffies_snap = ACCESS_ONCE(jiffies); > > Why do you need to snapshot jiffies in this version but not in the > version you originally posted?
Because in the original, the maximum error was one second, which was not worth worrying about.
> > while (ULONG_CMP_LT(jiffies_snap, shutdown_time) && > > !kthread_should_stop()) { > > delta = shutdown_time - jiffies_snap; > > if (verbose) > > printk(KERN_ALERT "%s" TORTURE_FLAG > > "rcu_torture_shutdown task: %lu " > > "jiffies remaining\n", > > torture_type, delta); > > I suggested dropping this print entirely; under normal circumstances it > should never print. It will only print if > schedule_timeout_interruptible wakes up spuriously.
OK, I can qualify with a firsttime local variable.
> > schedule_timeout_interruptible(delta); > > jiffies_snap = ACCESS_ONCE(jiffies); > > } > > Any reason this entire loop body couldn't just become > msleep_interruptible()?
Aha!!! Because then it won't break out of the loop if someone does a rmmod of rcutorture. Which will cause the rmmod to hang until the thing decides that it is time to shut down the system. Which is why I need to do the sleep in smallish pieces -- I cannot sleep longer than I would be comfortable delaying the rmmod.
Which is why I think I need to revert back to the old version that did the schedule_timeout_interruptible(1).
> > if (ULONG_CMP_LT(jiffies_snap, shutdown_time)) { > > VERBOSE_PRINTK_STRING("rcu_torture_shutdown task stopping"); > > return 0; > > } > > Writing this as "if (kthread_should_stop())" seems clearer.
I don't have any real preference here, but as long as I need to back out the earlier changes, I might as well make this one. ;-)
Thanx, Paul
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