[PATCH v3 1/3] rcutorture: Allow a negative value for nfakewriters

Uladzislau Rezki (Sony)
2025-02-25T11:00:24Z

Currently "nfakewriters" parameter can be set to any value but
there is no possibility to adjust it automatically based on how
many CPUs a system has where a test is run on.

To address this, if the "nfakewriters" is set to negative it will
be adjusted to num_online_cpus() during torture initialization.

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
kernel/rcu/rcutorture.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index d98b3bd6d91f..f376262532ce 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -148,6 +148,7 @@ MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, srcu, ...)");

static int nrealnocbers;
static int nrealreaders;
+static int nrealfakewriters;
static struct task_struct *writer_task;
static struct task_struct **fakewriter_tasks;
static struct task_struct **reader_tasks;
@@ -1763,7 +1764,7 @@ rcu_torture_fakewriter(void *arg)
do {
torture_hrtimeout_jiffies(torture_random(&rand) % 10, &rand);
if (cur_ops->cb_barrier != NULL &&
- torture_random(&rand) % (nfakewriters * 8) == 0) {
+ torture_random(&rand) % (nrealfakewriters * 8) == 0) {
cur_ops->cb_barrier();
} else {
switch (synctype[torture_random(&rand) % nsynctypes]) {
@@ -2568,7 +2569,7 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
"nocbs_nthreads=%d nocbs_toggle=%d "
"test_nmis=%d "
"preempt_duration=%d preempt_interval=%d\n",
- torture_type, tag, nrealreaders, nfakewriters,
+ torture_type, tag, nrealreaders, nrealfakewriters,
stat_interval, verbose, test_no_idle_hz, shuffle_interval,
stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
test_boost, cur_ops->can_boost,
@@ -3644,7 +3645,7 @@ rcu_torture_cleanup(void)
rcu_torture_reader_mbchk = NULL;

if (fakewriter_tasks) {
- for (i = 0; i < nfakewriters; i++)
+ for (i = 0; i < nrealfakewriters; i++)
torture_stop_kthread(rcu_torture_fakewriter,
fakewriter_tasks[i]);
kfree(fakewriter_tasks);
@@ -4066,6 +4067,14 @@ rcu_torture_init(void)

rcu_torture_init_srcu_lockdep();

+ if (nfakewriters >= 0) {
+ nrealfakewriters = nfakewriters;
+ } else {
+ nrealfakewriters = num_online_cpus() - 2 - nfakewriters;
+ if (nrealfakewriters <= 0)
+ nrealfakewriters = 1;
+ }
+
if (nreaders >= 0) {
nrealreaders = nreaders;
} else {
@@ -4122,8 +4131,9 @@ rcu_torture_init(void)
writer_task);
if (torture_init_error(firsterr))
goto unwind;
- if (nfakewriters > 0) {
- fakewriter_tasks = kcalloc(nfakewriters,
+
+ if (nrealfakewriters > 0) {
+ fakewriter_tasks = kcalloc(nrealfakewriters,
sizeof(fakewriter_tasks[0]),
GFP_KERNEL);
if (fakewriter_tasks == NULL) {
@@ -4132,7 +4142,7 @@ rcu_torture_init(void)
goto unwind;
}
}
- for (i = 0; i < nfakewriters; i++) {
+ for (i = 0; i < nrealfakewriters; i++) {
firsterr = torture_create_kthread(rcu_torture_fakewriter,
NULL, fakewriter_tasks[i]);
if (torture_init_error(firsterr))
--
2.39.5