From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>
Subject: Re: [PATCH 2/9] timer: Add comments about calc_index() ceiling work
Date: Fri, 17 Jul 2020 14:55:56 +0200 [thread overview]
Message-ID: <20200717125555.GB25465@lenoir> (raw)
In-Reply-To: <87tuyav4qx.fsf@nanos.tec.linutronix.de>
On Tue, Jul 14, 2020 at 11:13:26AM +0200, Thomas Gleixner wrote:
> Frederic Weisbecker <frederic@kernel.org> writes:
> > static inline unsigned calc_index(unsigned expires, unsigned lvl)
> > {
> > + /*
> > + * Time may have past since the clock last reached an index of
> > + * this @lvl. And that time, below LVL_GRAN(@lvl), is going to
> > + * be substracted from the delta until we reach @expires. To
> > + * fix that we must add one level granularity unit to make sure
> > + * we rather expire late than early. Prefer ceil over floor.
>
> This comment confuses the hell out of me.
Me too...
>
> /*
> * The timer wheel has to guarantee that a timer does not fire
> * early. Early expiry can happen due to:
> * - Timer is armed at the edge of a tick
> * - Truncation of the expiry time in the outer wheel levels
> *
> * Round up with level granularity to prevent this.
> */
>
> Hmm?
That's relieving, I'm updating the patch.
Thanks!
next prev parent reply other threads:[~2020-07-17 12:56 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-07 1:32 [PATCH 0/9] timer: Reduce timers softirq v2 Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 1/9] timer: Move trigger_dyntick_cpu() to enqueue_timer() Frederic Weisbecker
2020-07-09 12:17 ` Anna-Maria Behnsen
2020-07-15 13:20 ` Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 2/9] timer: Add comments about calc_index() ceiling work Frederic Weisbecker
2020-07-14 9:13 ` Thomas Gleixner
2020-07-17 12:55 ` Frederic Weisbecker [this message]
2020-07-07 1:32 ` [PATCH 3/9] timer: Optimize _next_timer_interrupt() level iteration Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 4/9] timers: Always keep track of next expiry Frederic Weisbecker
2020-07-14 8:49 ` Anna-Maria Behnsen
2020-07-17 12:51 ` Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 5/9] timer: Reuse next expiry cache after nohz exit Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 6/9] timer: Expand clk forward logic beyond nohz Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 7/9] timer: Spare timer softirq until next expiry Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 8/9] timer: Remove must_forward_clk Frederic Weisbecker
2020-07-07 1:32 ` [PATCH 9/9] timer: Lower base clock forwarding threshold Frederic Weisbecker
2020-07-09 7:02 ` [PATCH 0/9] timer: Reduce timers softirq v2 Juri Lelli
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