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: [RFC PATCH 10/10] timer: Lower base clock forwarding threshold
Date: Fri, 3 Jul 2020 02:12:20 +0200 [thread overview]
Message-ID: <20200703001219.GD27417@lenoir> (raw)
In-Reply-To: <87zh8irltc.fsf@nanos.tec.linutronix.de>
On Thu, Jul 02, 2020 at 05:14:23PM +0200, Thomas Gleixner wrote:
> Frederic Weisbecker <frederic@kernel.org> writes:
> > On Thu, Jul 02, 2020 at 03:21:35PM +0200, Thomas Gleixner wrote:
> > The following part:
> >
> >> > * Also while executing timers, base->clk is 1 offset ahead
> >> > * of jiffies to avoid endless requeuing to current jffies.
> >> > */
> >
> > relates to situation when (long)(jnow - base->clk) < 0
>
> This still is inconsistent with your changelog:
Right.
>
> > There is no apparent reason for not forwarding base->clk when it's 2
> > jiffies late
>
> Let's do the math:
>
> jiffies = 4
> base->clk = 2
>
> 4 - 2 = 2
>
> which means it is forwarded when it's 2 jiffies late with the original
> code, because 2 < 2.
>
> The reason for this < 2 is historical and goes back to the oddities of
> the original timer wheel before the big rewrite.
Ok. And is it still needed today or can we now forward even with a 1 delta?
next prev parent reply other threads:[~2020-07-03 0:12 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-01 1:10 [RFC PATCH 00/10] timer: Reduce timers softirq (and other optimizations) Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 01/10] timer: Prevent base->clk from moving backward Frederic Weisbecker
2020-07-01 16:35 ` Juri Lelli
2020-07-01 23:20 ` Frederic Weisbecker
2020-07-02 9:59 ` Juri Lelli
2020-07-02 14:04 ` Frederic Weisbecker
2020-07-02 14:32 ` Frederic Weisbecker
2020-07-02 15:57 ` Juri Lelli
2020-07-02 9:48 ` Thomas Gleixner
2020-07-01 1:10 ` [RFC PATCH 02/10] timer: Move trigger_dyntick_cpu() to enqueue_timer() Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 03/10] timer: Simplify LVL_START() and calc_index() Frederic Weisbecker
2020-07-02 11:59 ` Thomas Gleixner
2020-07-02 12:27 ` Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 04/10] timer: Optimize _next_timer_interrupt() level iteration Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 05/10] timers: Always keep track of next expiry Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 06/10] timer: Reuse next expiry cache after nohz exit Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 07/10] timer: Expand clk forward logic beyond nohz Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 08/10] timer: Spare timer softirq until next expiry Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 09/10] timer: Remove must_forward_clk Frederic Weisbecker
2020-07-01 1:10 ` [RFC PATCH 10/10] timer: Lower base clock forwarding threshold Frederic Weisbecker
2020-07-02 13:21 ` Thomas Gleixner
2020-07-02 13:32 ` Frederic Weisbecker
2020-07-02 15:14 ` Thomas Gleixner
2020-07-03 0:12 ` Frederic Weisbecker [this message]
2020-07-03 9:13 ` Thomas Gleixner
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