linux-kernel - Re: [PATCH v4 14/16] timer: Implement the hierarchical pull model

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Message-ID: <a1e17785-8a8b-2d42-bc66-73d8e263b9b@linutronix.de>
Date:   Thu, 10 Nov 2022 07:34:14 +0100 (CET)
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <jstultz@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arjan van de Ven <arjan@...radead.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v4 14/16] timer: Implement the hierarchical pull model

On Wed, 9 Nov 2022, Frederic Weisbecker wrote:

> On Fri, Nov 04, 2022 at 03:57:35PM +0100, Anna-Maria Behnsen wrote:
> > diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> > index f8b2065df79b..214397d84747 100644
> > --- a/kernel/time/timer.c
> > +++ b/kernel/time/timer.c
> > @@ -53,6 +53,7 @@
> >  #include <asm/io.h>
> >  
> >  #include "tick-internal.h"
> > +#include "timer_migration.h"
> >  
> >  #define CREATE_TRACE_POINTS
> >  #include <trace/events/timer.h>
> > @@ -592,10 +593,13 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
> >  
> >  	/*
> >  	 * We might have to IPI the remote CPU if the base is idle and the
> > -	 * timer is not deferrable. If the other CPU is on the way to idle
> > -	 * then it can't set base->is_idle as we hold the base lock:
> > +	 * timer is pinned. If it is a non pinned timer, it is only queued
> > +	 * on the remote CPU, when timer was running during queueing. Then
> > +	 * everything is handled by remote CPU anyway.
> > +	 * on the way to idle then it can't set base->is_idle as we hold
> > +	 * the base lock:
> >  	 */
> > -	if (base->is_idle)
> > +	if (base->is_idle && timer->flags & TIMER_PINNED)
> >  		wake_up_nohz_cpu(base->cpu);
> 
> I'm probably missing something but, shouldn't there be a call to
> tmigr_new_timer() on the target to handle the new non-pinned timer?
> 

We need to keep the original way right now. This TIMER_PINNED condition is
valid only when enqueue on local CPU is in place.