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rcutorture: Test runtime toggling of CPUs' callback offloading

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Frederic Weisbecker is adding the ability to change the rcu_nocbs state
of CPUs at runtime, that is, to offload and deoffload their RCU callback
processing without the need to reboot.  As the old saying goes, "if it
ain't tested, it don't work", so this commit therefore adds prototype
rcutorture testing for this capability.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-09-23 17:39:46 -07:00
parent dcd42591eb
commit 2c4319bd1d
2 changed files with 95 additions and 3 deletions
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8
Documentation/admin-guide/kernel-parameters.txt
View File

@ -4338,6 +4338,14 @@
stress RCU, they don't participate in the actual
test, hence the "fake".
rcutorture.nocbs_nthreads= [KNL]
Set number of RCU callback-offload togglers.
Zero (the default) disables toggling.
rcutorture.nocbs_toggle= [KNL]
Set the delay in milliseconds between successive
callback-offload toggling attempts.
rcutorture.nreaders= [KNL]
Set number of RCU readers. The value -1 selects
N-1, where N is the number of CPUs. A value

90
kernel/rcu/rcutorture.c
View File

@ -97,6 +97,8 @@ torture_param(int, object_debug, 0,
torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
torture_param(int, onoff_interval, 0,
"Time between CPU hotplugs (jiffies), 0=disable");
torture_param(int, nocbs_nthreads, 0, "Number of NOCB toggle threads, 0 to disable");
torture_param(int, nocbs_toggle, 1000, "Time between toggling nocb state (ms)");
torture_param(int, read_exit_delay, 13,
"Delay between read-then-exit episodes (s)");
torture_param(int, read_exit_burst, 16,
@ -127,10 +129,12 @@ static char *torture_type = "rcu";
module_param(torture_type, charp, 0444);
MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, srcu, ...)");
static int nrealnocbers;
static int nrealreaders;
static struct task_struct *writer_task;
static struct task_struct **fakewriter_tasks;
static struct task_struct **reader_tasks;
static struct task_struct **nocb_tasks;
static struct task_struct *stats_task;
static struct task_struct *fqs_task;
static struct task_struct *boost_tasks[NR_CPUS];
@ -174,6 +178,8 @@ static unsigned long n_read_exits;
static struct list_head rcu_torture_removed;
static unsigned long shutdown_jiffies;
static unsigned long start_gp_seq;
static atomic_long_t n_nocb_offload;
static atomic_long_t n_nocb_deoffload;
static int rcu_torture_writer_state;
#define RTWS_FIXED_DELAY 0
@ -1498,6 +1504,53 @@ rcu_torture_reader(void *arg)
return 0;
}
/*
* Randomly Toggle CPUs' callback-offload state. This uses hrtimers to
* increase race probabilities and fuzzes the interval between toggling.
*/
static int rcu_nocb_toggle(void *arg)
{
int cpu;
int maxcpu = -1;
int oldnice = task_nice(current);
long r;
DEFINE_TORTURE_RANDOM(rand);
ktime_t toggle_delay;
unsigned long toggle_fuzz;
ktime_t toggle_interval = ms_to_ktime(nocbs_toggle);
VERBOSE_TOROUT_STRING("rcu_nocb_toggle task started");
while (!rcu_inkernel_boot_has_ended())
schedule_timeout_interruptible(HZ / 10);
for_each_online_cpu(cpu)
maxcpu = cpu;
WARN_ON(maxcpu < 0);
if (toggle_interval > ULONG_MAX)
toggle_fuzz = ULONG_MAX >> 3;
else
toggle_fuzz = toggle_interval >> 3;
if (toggle_fuzz <= 0)
toggle_fuzz = NSEC_PER_USEC;
do {
r = torture_random(&rand);
cpu = (r >> 4) % (maxcpu + 1);
if (r & 0x1) {
rcu_nocb_cpu_offload(cpu);
atomic_long_inc(&n_nocb_offload);
} else {
rcu_nocb_cpu_deoffload(cpu);
atomic_long_inc(&n_nocb_deoffload);
}
toggle_delay = torture_random(&rand) % toggle_fuzz + toggle_interval;
set_current_state(TASK_INTERRUPTIBLE);
schedule_hrtimeout(&toggle_delay, HRTIMER_MODE_REL);
if (stutter_wait("rcu_nocb_toggle"))
sched_set_normal(current, oldnice);
} while (!torture_must_stop());
torture_kthread_stopping("rcu_nocb_toggle");
return 0;
}
/*
* Print torture statistics. Caller must ensure that there is only
* one call to this function at a given time!!! This is normally
@ -1553,7 +1606,9 @@ rcu_torture_stats_print(void)
data_race(n_barrier_successes),
data_race(n_barrier_attempts),
data_race(n_rcu_torture_barrier_error));
pr_cont("read-exits: %ld\n", data_race(n_read_exits));
pr_cont("read-exits: %ld ", data_race(n_read_exits));
pr_cont("nocb-toggles: %ld:%ld\n",
atomic_long_read(&n_nocb_offload), atomic_long_read(&n_nocb_deoffload));
pr_alert("%s%s ", torture_type, TORTURE_FLAG);
if (atomic_read(&n_rcu_torture_mberror) ||
@ -1647,7 +1702,8 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
"stall_cpu_block=%d "
"n_barrier_cbs=%d "
"onoff_interval=%d onoff_holdoff=%d "
"read_exit_delay=%d read_exit_burst=%d\n",
"read_exit_delay=%d read_exit_burst=%d "
"nocbs_nthreads=%d nocbs_toggle=%d\n",
torture_type, tag, nrealreaders, nfakewriters,
stat_interval, verbose, test_no_idle_hz, shuffle_interval,
stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
@ -1657,7 +1713,8 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
stall_cpu_block,
n_barrier_cbs,
onoff_interval, onoff_holdoff,
read_exit_delay, read_exit_burst);
read_exit_delay, read_exit_burst,
nocbs_nthreads, nocbs_toggle);
}
static int rcutorture_booster_cleanup(unsigned int cpu)
@ -2500,6 +2557,13 @@ rcu_torture_cleanup(void)
torture_stop_kthread(rcu_torture_stall, stall_task);
torture_stop_kthread(rcu_torture_writer, writer_task);
if (nocb_tasks) {
for (i = 0; i < nrealnocbers; i++)
torture_stop_kthread(rcu_nocb_toggle, nocb_tasks[i]);
kfree(nocb_tasks);
nocb_tasks = NULL;
}
if (reader_tasks) {
for (i = 0; i < nrealreaders; i++)
torture_stop_kthread(rcu_torture_reader,
@ -2762,6 +2826,26 @@ rcu_torture_init(void)
if (firsterr)
goto unwind;
}
nrealnocbers = nocbs_nthreads;
if (WARN_ON(nrealnocbers < 0))
nrealnocbers = 1;
if (WARN_ON(nocbs_toggle < 0))
nocbs_toggle = HZ;
if (nrealnocbers > 0) {
nocb_tasks = kcalloc(nrealnocbers, sizeof(nocb_tasks[0]), GFP_KERNEL);
if (nocb_tasks == NULL) {
VERBOSE_TOROUT_ERRSTRING("out of memory");
firsterr = -ENOMEM;
goto unwind;
}
} else {
nocb_tasks = NULL;
}
for (i = 0; i < nrealnocbers; i++) {
firsterr = torture_create_kthread(rcu_nocb_toggle, NULL, nocb_tasks[i]);
if (firsterr)
goto unwind;
}
if (stat_interval > 0) {
firsterr = torture_create_kthread(rcu_torture_stats, NULL,
stats_task);