linux-kernel - Re: [RFC][PATCH 2/2] time: alarmtimer: Use TASK

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Date:   Fri, 24 Feb 2023 11:02:49 +0100
From:   Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <jstultz@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Michael <michael@...isi.de>, kernel-team@...roid.com,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [RFC][PATCH 2/2] time: alarmtimer: Use TASK_FREEZABLE to cleanup
 freezer handling

Hi Thomas

On Tue, Feb 21, 2023 at 8:10 AM Michael Nazzareno Trimarchi
<michael@...rulasolutions.com> wrote:
>
> Hi
>
> On Tue, Feb 21, 2023 at 1:12 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > Michael!
> >
> > On Mon, Feb 20 2023 at 22:32, Michael Nazzareno Trimarchi wrote:
> > > On Mon, Feb 20, 2023 at 10:18 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> > >>   * alarmtimer_fired - Handles alarm hrtimer being fired.
> > >> @@ -194,6 +196,8 @@ static enum hrtimer_restart alarmtimer_f
> > >>         int ret = HRTIMER_NORESTART;
> > >>         int restart = ALARMTIMER_NORESTART;
> > >>
> > >> +       atomic_inc(&alarmtimer_wakeup);
> > >> +
> > >
> > >        ptr->it_active = 0;
> > >         if (ptr->it_interval) {
> > >                 atomic_inc(&alarmtimer_wakeup);
> > >                 si_private = ++ptr->it_requeue_pending;
> > >         }
> > >
> > > Should I not go to the alarm_handle_timer? and only if it's a periodic
> > > one?
> >
> > Why?
> >
>
> You are right. I will pay more attention to my reply.
>

I get time to test it and if the system suspend to ram we need to catch:

case PM_SUSPEND_PREPARE:
case PM_POST_SUSPEND:

Michael

> Michael
>
> > Any alarmtimer which hits that window has exactly the same problem.
> >
> > It's not restricted to periodic timers. Why would a dropped one-shot
> > wakeup be acceptable?
> >
> > It's neither restricted to posix timers. If a clock_nanosleep(ALARM)
> > expires in that window then the task wake up will just end up in the
> > /dev/null bucket for the very same reason. Why would this be correct?
> >
> > Hmm?
> >
> > <GRMBL>
> > > Michael
> > >
> > >>         spin_lock_irqsave(&base->lock, flags);
> >
> > <SNIP>Tons of wasted electrons</SNIP>
> >
> > Can you please trim your replies?
> >
> > </GRMBL>
> >
> > Thanks,
> >
> >         tglx