linux-kernel - RE: [PATCH] rcutorture: Create nocb tasks only for CONFIG_RCU_NOCB

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Date:   Thu, 2 Feb 2023 06:54:45 +0000
From:   "Zhang, Qiang1" <qiang1.zhang@...el.com>
To:     "Zhang, Qiang1" <qiang1.zhang@...el.com>,
        "paulmck@...nel.org" <paulmck@...nel.org>,
        "frederic@...nel.org" <frederic@...nel.org>,
        "quic_neeraju@...cinc.com" <quic_neeraju@...cinc.com>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>
CC:     "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] rcutorture: Create nocb tasks only for
 CONFIG_RCU_NOCB_CPU=y kernels

>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@...el.com>
>---
> kernel/rcu/rcutorture.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
>diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
>index 297da28ce92d..27becacbe3b2 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;
>+	}

Sorry, I ignored the case where the nocbs_nthreads is set to a negative value, will resend.

> 	if (cur_ops->init)
> 		cur_ops->init();
> 
>-- 
2.25.1