linux-kernel - Re: [PATCH 3/3] tick/nohz: Don't shutdown the lowres tick from itself

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZLHh71KIIioR85aa@lothringen>
Date:   Sat, 15 Jul 2023 02:01:51 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] tick/nohz: Don't shutdown the lowres tick from itself

On Fri, Jul 14, 2023 at 02:44:49PM -0400, Joel Fernandes wrote:
> On 7/14/23 08:08, Frederic Weisbecker wrote:
> One slight concern here though, where in the idle loop is the removed
> statement "tick_program_event(KTIME_MAX, 1);" happening if the tick was
> already stopped before? If it is happening in tick_nohz_stop_tick(), don't
> we early return from there and avoid doing that
> "tick_program_event(KTIME_MAX, 1);" altogether, if the tick was already
> stopped and the next event has not changed?
> 
>         /* Skip reprogram of event if its not changed */
>         if (ts->tick_stopped && (expires == ts->next_tick)) {
>                 /* Sanity check: make sure clockevent is actually programmed */
>                 if (tick == KTIME_MAX || ts->next_tick ==  [...]
>                         return;
> 		[...]
> 	}

Sure, if tick_program_event(KTIME_MAX, 1) was already called in the
previous idle loop iteration, then there is no need to call that again.

Or am I missing something else?

> 
> Also just a nit, here you can remove indent by doing:
> 
> if (unlikely(ts->tick_stopped))
>     return;
> hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
> tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
> 
> Which is pretty much the original code except for the tick_program_event().

Either I remove an indent or I remove a statement. I guess it's a matter of
personal taste. I don't mind either way :-)

Thanks.