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From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Tue, 12 Jul 2022 16:27:05 -0400
Message-ID: <CAEXW_YS8hrT78JG_2uQX38oaF5TEGz-M3EgJ2PWjx8g+cfmhBw@mail.gmail.com>
Subject: Re: [PATCH v2 6/8] rcuscale: Add test for using call_rcu_lazy() to
 emulate kfree_rcu()
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     rcu <rcu@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Rushikesh S Kadam <rushikesh.s.kadam@intel.com>,
        "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
        Neeraj upadhyay <neeraj.iitr10@gmail.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, vineeth@bitbyteword.org
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Precedence: bulk

Ah, with all the threads, I missed this one :(. Sorry about that.

On Fri, Jul 8, 2022 at 7:06 PM Paul E. McKenney <paulmck@kernel.org> wrote:

> > Currently I added a test like the following which adds a new torture type, my
> > thought was to stress the new code to make sure nothing crashed or hung the
> > kernel. That is working well except I don't exactly understand the total-gps
> > print showing 0, which the other print shows 1188 GPs. I'll go dig into that
> > tomorrow.. thanks!
> >
> > The print shows
> > TREE11 ------- 1474 GPs (12.2833/s) [rcu_lazy: g0 f0x0 total-gps=0]
> > TREE11 no success message, 7 successful version messages
>
> Nice!!!  It is very good to see you correctly using the rcu_torture_ops
> facility correctly!
>
> And this could be good for your own testing, and I am happy to pull it
> in for that purpose (given it being fixed, having a good commit log,
> and so on).  After all, TREE10 is quite similar -- not part of CFLIST,
> but useful for certain types of focused testing.
>
> However, it would be very good to get call_rcu_lazy() testing going
> more generally, and in particular in TREE01 where offloading changes
> dynamically.  A good way to do this is to add a .call_lazy() component
> to the rcu_torture_ops structure, and check for it in a manner similar
> to that done for the .deferred_free() component.  Including adding a
> gp_normal_lazy module parameter.  This would allow habitual testing
> on a few scenarios and focused lazy testing on all of them via the
> --bootargs parameter.

Ok, if you don't mind I will make this particular enhancement to the
torture test in a future patchset, since I kind of decided on doing v3
with just fixes to what I have and more testing. Certainly happy to
enhance these tests in a future version.

> On the total-gps=0, the usual suspicion would be that the lazy callbacks
> never got invoked.  It looks like you were doing about a two-minute run,
> so maybe a longer run?  Though weren't they supposed to kick in at 15
> seconds or so?  Or did this value of zero come about because this run
> used exactly 300 grace periods?

It was zero because it required the RCU_FLAVOR torture type, where as
my torture type was lazy. Adding RCU_LAZY_FLAVOR to the list fixed it
:)

Thanks!

 - Joel


> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index 7120165a9342..cc6b7392d801 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -872,6 +872,64 @@ static struct rcu_torture_ops tasks_rude_ops = {
> >
> >  #endif // #else #ifdef CONFIG_TASKS_RUDE_RCU
> >
> > +#ifdef CONFIG_RCU_LAZY
> > +
> > +/*
> > + * Definitions for lazy RCU torture testing.
> > + */
> > +unsigned long orig_jiffies_till_flush;
> > +
> > +static void rcu_sync_torture_init_lazy(void)
> > +{
> > +     rcu_sync_torture_init();
> > +
> > +     orig_jiffies_till_flush = rcu_lazy_get_jiffies_till_flush();
> > +     rcu_lazy_set_jiffies_till_flush(50);
> > +}
> > +
> > +static void rcu_lazy_cleanup(void)
> > +{
> > +     rcu_lazy_set_jiffies_till_flush(orig_jiffies_till_flush);
> > +}
> > +
> > +static struct rcu_torture_ops rcu_lazy_ops = {
> > +     .ttype                  = RCU_LAZY_FLAVOR,
> > +     .init                   = rcu_sync_torture_init_lazy,
> > +     .cleanup                = rcu_lazy_cleanup,
> > +     .readlock               = rcu_torture_read_lock,
> > +     .read_delay             = rcu_read_delay,
> > +     .readunlock             = rcu_torture_read_unlock,
> > +     .readlock_held          = torture_readlock_not_held,
> > +     .get_gp_seq             = rcu_get_gp_seq,
> > +     .gp_diff                = rcu_seq_diff,
> > +     .deferred_free          = rcu_torture_deferred_free,
> > +     .sync                   = synchronize_rcu,
> > +     .exp_sync               = synchronize_rcu_expedited,
> > +     .get_gp_state           = get_state_synchronize_rcu,
> > +     .start_gp_poll          = start_poll_synchronize_rcu,
> > +     .poll_gp_state          = poll_state_synchronize_rcu,
> > +     .cond_sync              = cond_synchronize_rcu,
> > +     .call                   = call_rcu_lazy,
> > +     .cb_barrier             = rcu_barrier,
> > +     .fqs                    = rcu_force_quiescent_state,
> > +     .stats                  = NULL,
> > +     .gp_kthread_dbg         = show_rcu_gp_kthreads,
> > +     .check_boost_failed     = rcu_check_boost_fail,
> > +     .stall_dur              = rcu_jiffies_till_stall_check,
> > +     .irq_capable            = 1,
> > +     .can_boost              = IS_ENABLED(CONFIG_RCU_BOOST),
> > +     .extendables            = RCUTORTURE_MAX_EXTEND,
> > +     .name                   = "rcu_lazy"
> > +};
> > +
> > +#define LAZY_OPS &rcu_lazy_ops,
> > +
> > +#else // #ifdef CONFIG_RCU_LAZY
> > +
> > +#define LAZY_OPS
> > +
> > +#endif // #else #ifdef CONFIG_RCU_LAZY
> > +
> >
> >  #ifdef CONFIG_TASKS_TRACE_RCU
> >
> > @@ -3145,7 +3203,7 @@ rcu_torture_init(void)
> >       unsigned long gp_seq = 0;
> >       static struct rcu_torture_ops *torture_ops[] = {
> >               &rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops, &busted_srcud_ops,
> > -             TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
> > +             TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS LAZY_OPS
> >               &trivial_ops,
> >       };
> >
> > diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE11 b/tools/testing/selftests/rcutorture/configs/rcu/TREE11
> > new file mode 100644
> > index 000000000000..436013f3e015
> > --- /dev/null
> > +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE11
> > @@ -0,0 +1,18 @@
> > +CONFIG_SMP=y
> > +CONFIG_PREEMPT_NONE=n
> > +CONFIG_PREEMPT_VOLUNTARY=n
> > +CONFIG_PREEMPT=y
> > +#CHECK#CONFIG_PREEMPT_RCU=y
> > +CONFIG_HZ_PERIODIC=n
> > +CONFIG_NO_HZ_IDLE=y
> > +CONFIG_NO_HZ_FULL=n
> > +CONFIG_RCU_TRACE=y
> > +CONFIG_HOTPLUG_CPU=y
> > +CONFIG_MAXSMP=y
> > +CONFIG_CPUMASK_OFFSTACK=y
> > +CONFIG_RCU_NOCB_CPU=y
> > +CONFIG_DEBUG_LOCK_ALLOC=n
> > +CONFIG_RCU_BOOST=n
> > +CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
> > +CONFIG_RCU_EXPERT=y
> > +CONFIG_RCU_LAZY=y
> > diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot
> > new file mode 100644
> > index 000000000000..9b6f720d4ccd
> > --- /dev/null
> > +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot
> > @@ -0,0 +1,8 @@
> > +maxcpus=8 nr_cpus=43
> > +rcutree.gp_preinit_delay=3
> > +rcutree.gp_init_delay=3
> > +rcutree.gp_cleanup_delay=3
> > +rcu_nocbs=0-7
> > +rcutorture.torture_type=rcu_lazy
> > +rcutorture.nocbs_nthreads=8
> > +rcutorture.fwd_progress=0
> > --
> > 2.37.0.rc0.161.g10f37bed90-goog
> >