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

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Message-ID: <CAOf5uw=+yZiTXGyjDgiw_w9yZZ5Pz3JQpykdCyFfbpNBTz+rXA@mail.gmail.com>
Date:   Tue, 21 Feb 2023 08:10:38 +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

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.

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