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Date:   Wed, 6 May 2020 17:33:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 1 03/36] sched: Clean up scheduler_ipi()

On Wed, May 06, 2020 at 02:37:19PM +0200, Alexandre Chartre wrote:
> On 5/5/20 3:16 PM, Thomas Gleixner wrote:
> > @@ -650,6 +655,16 @@ static inline bool got_nohz_idle_kick(vo
> >   	return false;
> >   }
> > +static void nohz_csd_func(void *info)
> > +{
> > +	struct rq *rq = info;
> > +
> > +	if (got_nohz_idle_kick()) {
> > +		rq->idle_balance = 1;
> > +		raise_softirq_irqoff(SCHED_SOFTIRQ);
> > +	}
> > +}
> > +
> >   #else /* CONFIG_NO_HZ_COMMON */
> >   static inline bool got_nohz_idle_kick(void)

> >   #ifdef CONFIG_NO_HZ_COMMON
> >   		rq->last_blocked_load_update_tick = jiffies;
> >   		atomic_set(&rq->nohz_flags, 0);
> > +
> > +		rq_csd_init(rq, &rq->nohz_csd, nohz_csd_func);
> >   #endif
> >   #endif /* CONFIG_SMP */
> >   		hrtick_rq_init(rq);
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -10009,12 +10009,11 @@ static void kick_ilb(unsigned int flags)
> >   		return;
> >   	/*
> > -	 * Use smp_send_reschedule() instead of resched_cpu().
> > -	 * This way we generate a sched IPI on the target CPU which
> > +	 * This way we generate an IPI on the target CPU which
> >   	 * is idle. And the softirq performing nohz idle load balance
> >   	 * will be run before returning from the IPI.
> >   	 */
> > -	smp_send_reschedule(ilb_cpu);
> > +	smp_call_function_single_async(ilb_cpu, &cpu_rq(ilb_cpu)->wake_csd);
> 
> This should be nohz_csd instead of wake_csd, no? I.e.:
> 
>        smp_call_function_single_async(ilb_cpu, &cpu_rq(ilb_cpu)->nohz_csd);
> 

You figured correctly. Thanks!

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