linux-kernel - Re: [PATCH v4] rcutorture: Create nocb tasks only for rcu testing and CONFIG_RCU_NOCB

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Message-ID: <CAEXW_YR3F+hb4hWuaONM4qCqAkH_6MMBWKAaK7b2TAzodKhz8g@mail.gmail.com>
Date:   Fri, 3 Feb 2023 12:29:23 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     paulmck@...nel.org, frederic@...nel.org, quic_neeraju@...cinc.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org
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 <qiang1.zhang@...el.com> 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 <qiang1.zhang@...el.com>

Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

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
>