From: Josh Triplett <josh@joshtriplett.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com,
patches@linaro.org, "Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: [PATCH tip/core/rcu 2/9] rcu: Add rcutorture system-shutdown capability
Date: Wed, 16 Nov 2011 16:48:07 -0800 [thread overview]
Message-ID: <20111117004806.GA5201@leaf> (raw)
In-Reply-To: <20111116234358.GP2355@linux.vnet.ibm.com>
On Wed, Nov 16, 2011 at 03:43:58PM -0800, Paul E. McKenney wrote:
> 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.)
Which already handles compiling a kernel for you; ABAT just doesn't make
it as easy to compile userspace programs as it does for kernels. :)
> 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.
Done and attached.
> 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". ;-)
I actually think stat_interval makes perfect sense, as does runnable.
> > > 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.
The original shouldn't have an error either. If something incorrectly
caches jiffies, either version would sleep forever, not just for an
extra second.
> > > 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.
Oh, i see; it does print the very first time through. In that case, you
could move the print out of the loop entirely, rather than using a
"first time" flag.
> > > 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).
Does kthread_stop not interrupt an interruptible kthread? As far as I
can tell, rmmod of rcutorture currently finishes immediately, rather
than after all the one-second sleeps finish, which suggests that it
wakes up the threads in question.
- Josh Triplett
next prev parent reply other threads:[~2011-11-17 0:48 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-15 20:27 [PATCH tip/core/rcu 0/9] Preview of additional RCU changes for 3.3 Paul E. McKenney
2011-11-15 20:27 ` [PATCH tip/core/rcu 1/9] rcu: Permit RCU_FAST_NO_HZ to be used by TREE_PREEMPT_RCU Paul E. McKenney
2011-11-15 20:27 ` [PATCH tip/core/rcu 2/9] rcu: Add rcutorture system-shutdown capability Paul E. McKenney
2011-11-15 21:46 ` Josh Triplett
2011-11-16 20:32 ` Paul E. McKenney
2011-11-16 22:15 ` Josh Triplett
2011-11-16 22:44 ` Paul E. McKenney
2011-11-16 22:58 ` Josh Triplett
2011-11-16 23:43 ` Paul E. McKenney
2011-11-17 0:48 ` Josh Triplett [this message]
2011-11-17 0:49 ` Josh Triplett
2011-11-17 1:40 ` Paul E. McKenney
2011-11-17 23:57 ` Josh Triplett
2011-11-18 0:27 ` Paul E. McKenney
2011-11-15 20:27 ` [PATCH tip/core/rcu 3/9] rcu: Control rcutorture startup from kernel boot parameters Paul E. McKenney
2011-11-15 21:49 ` Josh Triplett
2011-11-16 20:38 ` Paul E. McKenney
2011-11-16 22:17 ` Josh Triplett
2011-11-15 20:28 ` [PATCH tip/core/rcu 4/9] sched: add is_idle_task() to handle invalidated uses of idle_cpu() Paul E. McKenney
2011-11-15 21:13 ` Josh Triplett
2011-11-16 19:54 ` Paul E. McKenney
2011-11-15 20:28 ` [PATCH tip/core/rcu 5/9] rcu: Make RCU use the new is_idle_task() API Paul E. McKenney
2011-11-15 21:35 ` Josh Triplett
2011-11-15 20:28 ` [PATCH tip/core/rcu 6/9] sparc: Make SPARC " Paul E. McKenney
2011-11-15 21:15 ` David Miller
2011-11-15 20:28 ` [PATCH tip/core/rcu 7/9] kdb: Make KDB " Paul E. McKenney
2011-11-15 20:28 ` [PATCH tip/core/rcu 8/9] events: Make events " Paul E. McKenney
2011-11-15 20:28 ` [PATCH tip/core/rcu 9/9] tile: Make tile " Paul E. McKenney
2011-11-23 17:03 ` Chris Metcalf
2011-11-28 23:02 ` Paul E. McKenney
2011-11-15 21:50 ` [PATCH tip/core/rcu 0/9] Preview of additional RCU changes for 3.3 Josh Triplett
2011-11-16 20:39 ` Paul E. McKenney
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