2023-02-03 06:36:40

by Zqiang

Subject: [PATCH v4] rcutorture: Create nocb tasks only for rcu testing and CONFIG_RCU_NOCB_CPU=y kernel

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 this is meaningless for non-rcu
testing or CONFIG_RCU_NOCB_CPU=n kernel create nocb tasks to periodically
toggle CPU's callback-offload state and adds unnecessary testing overhead.

This commit therefore add checks for cur_ops types and CONFIG_RCU_NOCB_CPU
options when nocbs_nthreads is non-zero to avoid unnecessary nocb task
creation.

Signed-off-by: Zqiang <[email protected]>
---
kernel/rcu/rcutorture.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 297da28ce92d..d01127e0e8cd 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -3708,6 +3708,12 @@ rcu_torture_init(void)
pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
fqs_duration = 0;
}
+ if (nocbs_nthreads != 0 && (cur_ops != &rcu_ops ||
+ !IS_ENABLED(CONFIG_RCU_NOCB_CPU))) {
+ pr_alert("rcu-torture types: %s and CONFIG_RCU_NOCB_CPU=%d, nocb toggle disabled.\n",
+ cur_ops->name, IS_ENABLED(CONFIG_RCU_NOCB_CPU));
+ nocbs_nthreads = 0;
+ }
if (cur_ops->init)
cur_ops->init();

--
2.25.1

2023-02-03 17:29:48

by Joel Fernandes

Subject: Re: [PATCH v4] rcutorture: Create nocb tasks only for rcu testing and CONFIG_RCU_NOCB_CPU=y kernel

On Fri, Feb 3, 2023 at 1:35 AM Zqiang <[email protected]> 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 this is meaningless for non-rcu
> testing or CONFIG_RCU_NOCB_CPU=n kernel create nocb tasks to periodically
> toggle CPU's callback-offload state and adds unnecessary testing overhead.
>
> This commit therefore add checks for cur_ops types and CONFIG_RCU_NOCB_CPU
> options when nocbs_nthreads is non-zero to avoid unnecessary nocb task
> creation.
>
> Signed-off-by: Zqiang <[email protected]>

Reviewed-by: Joel Fernandes (Google) <[email protected]>

thanks,

- Joel


> ---
> kernel/rcu/rcutorture.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 297da28ce92d..d01127e0e8cd 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -3708,6 +3708,12 @@ rcu_torture_init(void)
> pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
> fqs_duration = 0;
> }
> + if (nocbs_nthreads != 0 && (cur_ops != &rcu_ops ||
> + !IS_ENABLED(CONFIG_RCU_NOCB_CPU))) {
> + pr_alert("rcu-torture types: %s and CONFIG_RCU_NOCB_CPU=%d, nocb toggle disabled.\n",
> + cur_ops->name, IS_ENABLED(CONFIG_RCU_NOCB_CPU));
> + nocbs_nthreads = 0;
> + }
> if (cur_ops->init)
> cur_ops->init();
>
> --
> 2.25.1
>

2023-02-03 17:51:42

by Paul E. McKenney

Subject: Re: [PATCH v4] rcutorture: Create nocb tasks only for rcu testing and CONFIG_RCU_NOCB_CPU=y kernel

On Fri, Feb 03, 2023 at 12:29:23PM -0500, Joel Fernandes wrote:
> On Fri, Feb 3, 2023 at 1:35 AM Zqiang <[email protected]> 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 this is meaningless for non-rcu
> > testing or CONFIG_RCU_NOCB_CPU=n kernel create nocb tasks to periodically
> > toggle CPU's callback-offload state and adds unnecessary testing overhead.
> >
> > This commit therefore add checks for cur_ops types and CONFIG_RCU_NOCB_CPU
> > options when nocbs_nthreads is non-zero to avoid unnecessary nocb task
> > creation.
> >
> > Signed-off-by: Zqiang <[email protected]>
>
> Reviewed-by: Joel Fernandes (Google) <[email protected]>

Queued and pushed, thank you both!

Note that this loses testing of the offload/de-offload API when there
is nothing to offload or de-offload, but that is not necessarily the job
of rcutorture. Or if it is the job of rcutorture, perhaps it is a single
pair of calls somewhere. And that can certainly be a separate patch.

But perhaps Frederic has an opinion on what testing is needed for this
case, and if so where that testing should live.

Thanx, Paul

> thanks,
>
> - Joel
>
>
> > ---
> > kernel/rcu/rcutorture.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index 297da28ce92d..d01127e0e8cd 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -3708,6 +3708,12 @@ rcu_torture_init(void)
> > pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
> > fqs_duration = 0;
> > }
> > + if (nocbs_nthreads != 0 && (cur_ops != &rcu_ops ||
> > + !IS_ENABLED(CONFIG_RCU_NOCB_CPU))) {
> > + pr_alert("rcu-torture types: %s and CONFIG_RCU_NOCB_CPU=%d, nocb toggle disabled.\n",
> > + cur_ops->name, IS_ENABLED(CONFIG_RCU_NOCB_CPU));
> > + nocbs_nthreads = 0;
> > + }
> > if (cur_ops->init)
> > cur_ops->init();
> >
> > --
> > 2.25.1
> >