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

Joel Fernandes
2025-02-25T21:24:13Z

On Tue, Feb 25, 2025 at 12:00:18PM +0100, Uladzislau Rezki (Sony) wrote:
> 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, ...)");

IMO, this should also be updated to reflect the possibily to set it negative
and hence to number CPUs:

torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads");

thanks,

- Joel

>
> 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
>