linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Thomas Gleixner <tglx@linutronix.de>
To: Frederic Weisbecker <frederic@kernel.org>
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: Thu, 02 Jul 2020 17:14:23 +0200	[thread overview]
Message-ID: <87zh8irltc.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200702133219.GA27417@lenoir>

Frederic Weisbecker <frederic@kernel.org> writes:
> On Thu, Jul 02, 2020 at 03:21:35PM +0200, Thomas Gleixner wrote:
>> Frederic Weisbecker <frederic@kernel.org> writes:
>> > @@ -883,7 +883,7 @@ static inline void forward_timer_base(struct timer_base *base)
>> >  	 * Also while executing timers, base->clk is 1 offset ahead
>> >  	 * of jiffies to avoid endless requeuing to current jffies.
>> >  	 */
>> > -	if ((long)(jnow - base->clk) < 2)
>> > +	if ((long)(jnow - base->clk) < 1)
>> >  		return;
>> 
>> The apparent reason is in the comment right above the condition ...
>
> Hmm, that's a comment I added myself in the patch before.

:)

> 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:

> 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.

Thanks,

        tglx



  reply	other threads:[~2020-07-02 15:14 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 [this message]
2020-07-03  0:12         ` Frederic Weisbecker
2020-07-03  9:13           ` Thomas Gleixner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87zh8irltc.fsf@nanos.tec.linutronix.de \
    --to=tglx@linutronix.de \
    --cc=anna-maria@linutronix.de \
    --cc=frederic@kernel.org \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=peterz@infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).