From: Thomas Gleixner <tglx@linutronix.de>
To: Xu YiPing <xuyiping@hisilicon.com>
Cc: john.stultz@linaro.org, sboyd@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] timers: fix offset calculation when the expires align with LVL_GRAN
Date: Tue, 31 Jul 2018 16:22:15 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1807311616480.1610@nanos.tec.linutronix.de> (raw)
In-Reply-To: <c68d9944-1fcc-dcd5-1e3d-07f979323b8c@hisilicon.com>
On Tue, 31 Jul 2018, Xu YiPing wrote:
> On 2018/7/30 19:03, Thomas Gleixner wrote:
> >
> > __internal_add_timer(base, timer)
> > {
> > idx = calc_wheel_index(1, 1)
> > {
> > delta = 1 - 1; <- 0
> >
> > if (0 < LVL_START(1))
> > idx = calc_index(1, 0)
> > {
> > expires = (1 + LVL_GRAN(0) - 1) >> LVL_SHIFT(0);
> > ----> expires = 0
>
> LVL_GRAN(0) = 1 and LVL_SHIFT(0) = 0
>
> after the calculation, expires = 1 ?
Indeed. You're right. Math is hard... So the index would be 1 and still not
fulfil the below:
> > mod_timer(timer, jiffies + 1)
> >
> > will not fire before aty least one jiffy has elapsed. Let's look at the
> > time line:
> >
> > |-------------------|-------------------|----------------|
> > tick tick tick
> > jiffies jiffies + 1 jiffies + 2
> >
> > | |
> > | Any timer armed | ^
> > | here must be | |
> > | queued here -------------------------|
> >
> > in order to guarantee that. Timer wheel timers are not accurate and never
> > can be.
Thanks,
tglx
next prev parent reply other threads:[~2018-07-31 14:22 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-27 5:33 [PATCH] timers: fix offset calculation when the expires align with LVL_GRAN Xu YiPing
2018-07-30 11:03 ` Thomas Gleixner
2018-07-31 12:37 ` Xu YiPing
2018-07-31 13:45 ` Xu YiPing
2018-07-31 14:22 ` Thomas Gleixner [this message]
2018-07-31 14:34 ` Thomas Gleixner
2018-08-01 2:45 ` Xu YiPing
2018-08-01 7:10 ` Thomas Gleixner
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