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Date: Fri, 8 Jul 2022 04:25:09 +0000
From: Joel Fernandes <joel@...lfernandes.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
rushikesh.s.kadam@...el.com, urezki@...il.com,
neeraj.iitr10@...il.com, frederic@...nel.org, rostedt@...dmis.org,
vineeth@...byteword.org
Subject: Re: [PATCH v2 6/8] rcuscale: Add test for using call_rcu_lazy() to
emulate kfree_rcu()
On Sat, Jun 25, 2022 at 09:13:27PM -0700, Paul E. McKenney wrote:
> On Wed, Jun 22, 2022 at 10:51:00PM +0000, Joel Fernandes (Google) wrote:
> > Reuse the kfree_rcu() test in order to be able to compare the memory reclaiming
> > properties of call_rcu_lazy() with kfree_rcu().
> >
> > With this test, we find similar memory footprint and time call_rcu_lazy()
> > free'ing takes compared to kfree_rcu(). Also we confirm that call_rcu_lazy()
> > can survive OOM during extremely frequent calls.
> >
> > If we really push it, i.e. boot system with low memory and compare
> > kfree_rcu() with call_rcu_lazy(), I find that call_rcu_lazy() is more
> > resilient and is much harder to produce OOM as compared to kfree_rcu().
>
> Another approach would be to make rcutorture's forward-progress testing
> able to use call_rcu_lazy(). This would test lazy callback flooding.
>
> Yet another approach would be to keep one CPU idle other than a
> kthread doing call_rcu_lazy(). Of course "idle" includes redirecting
> those pesky interrupts.
>
> It is almost certainly necessary for rcutorture to exercise the
> call_rcu_lazy() path regularly.
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
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
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