> On Feb 2, 2023, at 1:57 AM, Zqiang <qiang1.zhang@xxxxxxxxx> wrote:
>
> When setting nocbs_nthreads to start rcutorture test with a non-zero value,
> the nocb tasks will be created and invoke rcu_nocb_cpu_offload/deoffload()
> to toggle CPU's callback-offload state, but for CONFIG_RCU_NOCB_CPU=n
> kernel, the rcu_nocb_cpu_offload/deoffload() is a no-op and this is also
> meaningless for torture_type is non-rcu.
>
> This commit therefore add member can_nocbs_toggle to rcu_torture_ops
> structure to avoid unnecessary nocb tasks creation.
>
> Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
> ---
> kernel/rcu/rcutorture.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
>Sorry if I am missing something but what is the point of adding more lines of code and complexity to handle this? Does it improve the test coverage or reduce overhead?
>
>This is test code. I see no problem with cost of an extra unused task with positive trade off of keeping the code simple…
For nocbs_nthreads is non-zero and CONFIG_RCU_NOCB_CPU=n kernels,
the rcu_nocb_cpu_offload/deoffload() is a no-op, we create nocbs_nthreads
kthreads and perform nocb toggle tests periodically, which is meaningless and
will take extra cpu time.
For non-rcu tests, it really doesn't make sense for us to turn on nocb toggle test.
Does this make the test a little more rigorous?
Thanks
Zqiang
>
>thanks,
>
> - Joel
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 297da28ce92d..ced0a8e1d765 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -383,6 +383,7 @@ struct rcu_torture_ops {
> long cbflood_max;
> int irq_capable;
> int can_boost;
> + int can_nocbs_toggle;
> int extendables;
> int slow_gps;
> int no_pi_lock;
> @@ -569,6 +570,7 @@ static struct rcu_torture_ops rcu_ops = {
> .stall_dur = rcu_jiffies_till_stall_check,
> .irq_capable = 1,
> .can_boost = IS_ENABLED(CONFIG_RCU_BOOST),
> + .can_nocbs_toggle = IS_ENABLED(CONFIG_RCU_NOCB_CPU),
> .extendables = RCUTORTURE_MAX_EXTEND,
> .name = "rcu"
> };
> @@ -2356,7 +2358,7 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
> "n_barrier_cbs=%d "
> "onoff_interval=%d onoff_holdoff=%d "
> "read_exit_delay=%d read_exit_burst=%d "
> - "nocbs_nthreads=%d nocbs_toggle=%d "
> + "nocbs_nthreads=%d/%d nocbs_toggle=%d "
> "test_nmis=%d\n",
> torture_type, tag, nrealreaders, nfakewriters,
> stat_interval, verbose, test_no_idle_hz, shuffle_interval,
> @@ -2368,7 +2370,7 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
> n_barrier_cbs,
> onoff_interval, onoff_holdoff,
> read_exit_delay, read_exit_burst,
> - nocbs_nthreads, nocbs_toggle,
> + nocbs_nthreads, cur_ops->can_nocbs_toggle, nocbs_toggle,
> test_nmis);
> }
>
> @@ -3708,6 +3710,10 @@ rcu_torture_init(void)
> pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
> fqs_duration = 0;
> }
> + if (!cur_ops->can_nocbs_toggle && nocbs_nthreads != 0) {
> + pr_alert("rcu-torture: ->can_nocbs_toggle false and non-zero nocbs_nthreads, nocbs_toggle disabled.\n");
> + nocbs_nthreads = 0;
> + }
> if (cur_ops->init)
> cur_ops->init();
>
> --
> 2.25.1
>
