linux-kernel - Re: [PATCH v2 1/4] sched/rt: Annotate the RT balancing logic irqwork as IRQ_WORK_HARD

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Date:   Wed, 13 Oct 2021 18:13:06 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v2 1/4] sched/rt: Annotate the RT balancing logic
 irqwork as IRQ_WORK_HARD_IRQ

On Wed,  6 Oct 2021 13:18:49 +0200
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> The push-IPI logic for RT tasks expects to be invoked from hardirq
> context. One reason is that a RT task on the remote CPU would block the
> softirq processing on PREEMPT_RT and so avoid pulling / balancing the RT
> tasks as intended.
> 
> Annotate root_domain::rto_push_work as IRQ_WORK_HARD_IRQ.
> 
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  kernel/sched/topology.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 4e8698e62f075..3d0157bd4e144 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -526,7 +526,7 @@ static int init_rootdomain(struct root_domain *rd)
>  #ifdef HAVE_RT_PUSH_IPI
>  	rd->rto_cpu = -1;
>  	raw_spin_lock_init(&rd->rto_lock);
> -	init_irq_work(&rd->rto_push_work, rto_push_irq_work_func);
> +	rd->rto_push_work = IRQ_WORK_INIT_HARD(rto_push_irq_work_func);

Should we not make an "init_irq_work_hard()" helper?

-- Steve

>  #endif
>  
>  	rd->visit_gen = 0;